Considering the fact that most of the problems sound gut related, I would suspect parasites. I would use ParaWellness Labs for specific reasons, mostly b/c most labs are inadequate in finding the problem.
Light sensitivity is also called photophobia - photophobia is linked to infectious organisms.
Sounds like the rashes, runny nose, skin itching etc are side effects from the immune reaction.
Drunk/high feeling could likely be immune related as well. For instance cytokines are released by the immune response which enter the blood/brain barrier and affect neurological processes.