First off, that doesn't at all look like blood to me, but rather the remnants of blueberries or raspberries, whatever it was that he ate, and it does look like poop, as AHBD already mentioned, not vomit, as it looks like a small bit of urate present in it. When they either vomit blood or pass it in their stools, it either shows up as being extremely dark in color (almost black), or if it's from active, internal bleeding it shows up as extremely bright red, oxygenated blood. This doesn't at all look like blood, it's pinkish/purple. And if he recently ate either blueberries or raspberries, I'd bet that he had a bowel movement and passed them in his stool/urate, especially if he's acting "normally".
That being said, your dragon is extremely small for being 2.5 years old, and if you've had him under a compact Reptisun 10.0
UVB bulb his entire life, and that is most likely on top of a mesh lid that is blocking 40% of the already far too weak UVB/UVA light for any Desert Reptile, let along a Bearded Dragon, that means that he has pretty much gotten no UVB or UVA light at all his entire life. This is the explanation for his stunted size and what is most likely a severe calcium deficiency and MBD. It's also most likely why he's not properly digesting his food, resulting in what you're seeing here. I'd ask you how old the compact Reptisun 10.0
UVB bulb you have is (they stop emitting any
UVB light at all at 6 months old and must be replaced) or how far away it is from his Basking Spot/Platform (they must be within about 4" unobstructed by the mesh or anything else to emit adequate UVB or UVA light to a Bearded Dragon), but just using a compact Reptisun 10.0
UVB light that is only 13 watts and is probably being blocked by a mesh lid means he's gotten no UVB or UVA light anyway, so the details of it's set-up or age don't really matter anyway. Also, you must dust his live insects in a Reptile-Grade calcium powder at least 4-5 times a week and in a Reptile-Grade Multivitamin at least 3 times a week for a Bearded Dragon's entire life; once a week is not nearly enough for either, but again, unless he's under a strong, adequate UVB tube that is unobstructed by a mesh lid/plastic safety cover on the tube fixture, is within the correct distance from his Basking Spot/Platform (T8 UVB tube needs to be within at least 6" and a much stronger T5 UVB tube, which is absolutely what you must buy him immediately, along with a matching length, T5-rated tube fixture with a metal reflector inside it, must be within at least 11" of his Basking Spot/Platform), and is replaced every 6 months for a weaker T8 tube and every 12 months for a much stronger T5 tube, then it doesn't matter how often you dust his insects in either powder, as he cannot absorb nor process/use any of it, it's simply being excreted in his bowel movements, along with most all of the vitamins, minerals, and nutrition he's eating in his food and supplements.
You really need to go onto Amazon.com (cheapest place by far) and order at least a 22" Reptisun 10.0 T5HO UVB tube or a 24" Arcadia 12% T5 UVB tube, along with a 24" (for either brand) T5-rated tube fixture for it immediately, as this is surely the start of the signs/symptoms of a severe calcium deficiency and MBD showing up, and he'll only get worse and worse. I don't know exactly how much the 24" Arcadia 12% T5 UVB tube costs, but on Amazon.com you can buy a 22" (shortest you should buy, don't bother with the 16" because the wattage is actually lower and he needs a very strong UVB tube to try to reverse any damage possible) a 22" Reptisun 10.0 T5HO UVB tube for around $24 and then the cheapest 24" tube fixture that is rated for a 24 watt, T5 tube that has a Metal Reflector included in it costs $28 on Amazon.com. So you can order both for around $50 shipped and have them within the week. For comparison, they don't sell the Reptisun 10.0 T5HO tubes in Petco or Petsmart, all they sell is either a package deal that includes a T5 rated light hood and a 5.0 T5HO UVB tube, which is only a 5% UVB tube and not much better than what you're using now, for $60, and then both Petco and Petsmart sell just an 18" Reptisun 10.0 T8 UVB tube for $37.99 just for the tube without a fixture, and honestly, not only would it be silly to order a T8 UVB tube that is weaker and needs to be replaced every 6 months for almost as much money as the stronger, longer T5 10.0 tube and a fixture for it cost, but your Dragon really needs the stronger T5 UVB tube ASAP.
In the meantime, again I don't know how old the compact 10.0
UVB bulb you have is, but if it's less than 6 months old and it's not causing him any eye or neurological issues, you need to remove the mesh lid and get the bulb within at least 6" of him for the time being, until the adequate T5 UVB tube is shipped to you. If the compact 10.0
UVB bulb is over 6 months old then it's not emitting any UVB or UVA light anyway...
Please get him a T5 UVB tube and fixture ordered ASAP and get it set up over the Hot Side of his tank, right alongside his bright-white colored Basking Bulb (not end-to-end but both right alongside each other sharing the Hot Side of the tank), and then get his Basking Spot/Platform set up directly underneath both lights so that he gets both at the same time while he basks, this is replicating natural sunlight as closely as possible.
I'm sure he's had some uvb, couldn't develop stable bones + grow like he has without it.
