Have you noticed, along with these hiccups, that your little guy has been sitting up very straight in his tank, and spending extended periods of time staring up at his lights? Or have you noticed him frequently sleeping in a standing position, leaning up against the glass in his tank, or propping his head up on pieces of his cage furniture while he sleeps, either at night, or during the daytime hours? You may also hear some popping sounds from your beardie when he breathes, but not always, and you usually are not able to hear them unless you have him perched on your shoulder, up near your ear.
If so, then he has most likely developed an Upper Respiratory Infection, and will need to be seen by a vet as soon as possible, so that he can be placed on an appropriate antibiotic before he becomes any worse. Baytril is usually the drug of choice for bearded dragons, and it works very well, and very quickly, once you begin to dose them with it. However, if he is starting with an Upper Respiratory Infection, then you need to have him seen very quickly, as once you begin to see these symptoms, they can become worse and they can develop pneumonia very quickly, which can be life threatening.
Beardies, like most other reptiles, are very adept at hiding their symptoms from us, and usually, by the time that you determine that there is something seriously wrong, they are extremely sick. My advice would be to have him checked out by your vet just as soon as you possibly can, for this reason.
Until you are able to get him a vet appointment, I would make sure that you keep him very well
hydrated, especially if he hasn't been eating properly for you. You can do this by either soaking him in extremely warm water for 15-20 minutes, twice a day, or by syringe feeding him 3 or 4 feeding syringes full of liquid twice daily. Doing the twice daily soaks will definitely be less stressful for him, and is an excellent way to make sure that he get the fluid that he needs, as beardies have the ability to absorb the moisture that their bodies need through their vent when they are submersed in water. Just be sure that you don't allow the water to get cold, and make sure to dry him very well before returning him to the basking spot in his tank. Also, do not leave him unattended in the water while he's soaking, since, if his head goes under, he could aspirate water into his lungs and drown. If he puts his head under by choice, and his mouth is moving, then he is
drinking the water on his own, which is fine, but if he is simply acting like he's sleeping and allowing his head to go under, then you need to intervene and support his head with your hand to keep him from aspirating water into his lungs. This extra fluid will go a long way as far as thinning out the secretions in his lungs, if he does have an Upper Respiratory Infection, and will help him not to get any worse until you can have him seem by your vet.
Also, if you can syringe feed him some type of low suger juice (such as apple juice or grape juice) a couple of times a day, the Vitamin C in the juice will help his system to fight off the infection. However, if you do opt to syringe feed him, only give him a few drops at a time, and put the syringe into the side of his mouth, about halfway back, when you give it to him. When administering fluids in this manner, they are much less likely to choke, as feeding from the side will not trigger their gag reflex, and also they are not able to spit it out, and they must swallow it. However, if your beardie is an adult, be very careful to only insert enough of the syringe to get the fluid into his mouth, and not enough so that he can get hold of the syringe with his teeth, or he could bite off the tip and swallow it, then you'll have a whole new set of problems. I usually use a pair of wire cutters to trim a portion of the tip off the end of the feeding syringe, and then use an emery board to smooth off the rough edges, which is much easier than having a tug of war with him if he gets agitated with you for force feeding him the liquid. He may take it very nicely for you, with no problem, as most of them seem to like juice, but, if he balks, you can still get it into him in the way that I described above, if you have to.
Please keep us posted on how he's doing, and let us know what the vet has to say.