My birthday was yesterday and my amazing friends took me to see the ocean! I sprayed myself down, but after a day of making a giant sand castle I was reminded that my swimsuit was a tankini. Right over my backside I have a giant swelling stripe and it's so painful that I can barely sleep on my back! I was given something called desitin but it doesn't seem to do much but numb it some.

Is there any way I can get it to heal it quickly with the budget of a poor college kid?

The best thing to help make a sunburn feel better is aloe vera.. you can find some lotion with it in it or just some plain aloe vera. It soothes the pain and makes it feel some better. You may have to just let it rub out on it's own if you can't get any lotion or aloe vera.

In addition to aloe vera, don't forget regular hydrating lotion once the pain is gone. A sunburn ultimately makes your sking very dry and it will peel off.

Like everyone else has said, aloe vera.

If you can't find it, though, something else you can do that doesn't really cost much is to add 3/4 of a cup of baking soda and half a cup of dry oatmeal to a lukewarm bath and soak in it for about 20 minutes. This takes the burn out, reduces swelling if it was a BAD sunburn, and generally eases the pain and promotes healing. YOu might feel a little goopy while in the bath, but getting rid of the hurt overrides that. 

If you don't have access to a bath, you can make a plaster, too. Take plastic wrap (the non-sticky kind) or a hand towel (iiiif you don't mind having to hand-wash gunk out of it).  Mix up a goopy-consistency paste of baking soda, dry oatmeal, and warm water in a bowl, pour it into the wrap or towel, and plaster it to your backside for about 20 minutes. Works in the shower or if you're sitting down. Works about the same, though it feels more gross than the bath.