Your leo needs to go to the vet asap, please do not delay, it could cost him his life.
Having said that...yes you definately want to up the temps in your tank. They should be around 85-90degrees on the hot side. Adding a heat bulb (buy a clamp lamp from wall mart and use a regular household bulb. Make sure your temperature reading is acurate, if you are using a stick-on-dial thermometer, or a stick-on-strip thermometer then they could be misreading as much as 20degrees. You need to use a digital thermometer to get an acurate reading, these can be purchased at wal-mart for about 6$. The indoor/outdoor ones work well as they have a "probe" you can fasten in the tank to get a quick acurate reading of any part of the tank.
You want to be giving him a straight calcium supplement, leave some in a dish 3x a week for him to lick and dust his crickets with it every time you feed. (as he gets older you willn eed to cut back on the amount of calcium) Only use the Vitimin powder with D3 2x weekly as too much D3 can be really bad.
As someone mentioned above you will want to add a humid hide, and i think probably another dry hide just for variety.
If he is eating crickets will the legs off continue to feed him this way, if he is eating then there is no need to force feed.
It is strange he might be impacted since he is on carpet, but it sounds like he is becasuse of the lack of fecal matter. Give him some warm water soaks to try and alleviate the impaction.
If he does poop, bring the fecal to the vet within 24 hours to have a parasite check run. Not that parasites would cause him to not use his back legs, but its a good thing to do anyway.
Your leo will not get better until his husbandry has been corrected. And he will not get better without help from a vetrinarian. Find a good reptile vt in your area and set up an appointment asap. Make sure to tell the vet on the phone the leo has not pooped in two weeks, this should get you an appointment on the same day. Correct his husbandry while you are waiting for the appointment.
Good luck
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0.1 Bearded dragon
0.1 mexican kingsnake
1.0.2 Leopard Gecko's
0.0.1 Rose Hair Tarantula
1.0 BTS
0.0.1 Reverse Okeetee Corn
0.1 Bullmastiff
4.1 Cats