What type of thermometer are you using, the only 2 ways to get an accurate reading are with either a temperature gun or a digital thermometer that has a long wire & probe on the end. A 75 watt seems a little too hot for a 10 gallon tank as I was only using a 60 watt when I had a 20 gallon set up, that's why I suspect you're not getting a good reading.
If your room temp doesn't drop below 65 degrees at night, you don't need to use anything while he sleeps. A temp of about 90 at night is actually too warm, they need to be cooler at night. If your room temp does drop below 65, then you could use a ceramic heat emitter that gives off heat but no light.
Since you're had your beardie for about a month, you really need to get a
UVB light very soon. Because he is a baby, right now is a critical time for his bone development and without UVB, he won't develop those strong bones. Here's a site that has the best fluorescent UVB you can get if you live in the USA:
http://www.petmountain.com/product/bulbs/504983/zoo-med-reptisun-10.0-high-output-uvb-bulb.html They are a very good company to deal with & this is the cheapest place you can find this bulb.
Since it seems like your tank temps might be too high, you should consider giving him a
bath 3 to 4 times a wk with his vent area (where he poos) right down in the water for about 15 min as you don't want him to get dehydrated which can happen very quickly with babies.
Since he is so small, you should be using the small sized crickets. They shouldn't be any larger than the space between his eyes. How many crickets do you offer him a day? Are you offering fresh veggies/greens daily too?