First, if you are a full time sudent, dont have health insurance and only work part time you should be able to get medicaide - and get the colonoscopy.
Colonoscopy might not tell you much unless you are looking for tumor, physical defects anyway.
But, why don't you take things one step at a time, going from simple cures to more intensive.
First try repopulating your gut flora with yogurt, good probiotics, make homemade saurkraut & eat a bit with every meal, and dont eat junk.
Do this religiously for 3 weeks and see if you notice any difference.
If not, move on to something like Dr. Sutter protocol with Barefoot's dewormer.
Then there are pharmaceuticals. If you know you have parasites, find a Dr who can diagnose, then research what meds treat them - and hit them hard like ICU says. many meds are available from pet/vet supply. But don't jump into that right away. And do your research first on PubMed, etc
Honestly, see if healthy gut flora make a difference first.
Hope that makes sense,
PS - my vitamin D is 10 - intentionally low for a protocol I'm on. There is no problem with Low vit D. It is just a medical fad that cropped up about 8 yrs ago.