In answer to your questions about sups/chemicals:
Before I say anything else, I want to be clear on something: At 18, and from what you’ve said so far, this shit is all in your head. I don’t think you should start relying on sups and chemicals at this stage—get to the root of what’s going on in your head so you can enjoy a long, natural, healthy sex life before resorting to external measures.
That said, look into yohimbe, maca, horny goat weed, tribulus, and tongkat ali. Use these sups as a last resort, and do your research before trying any of them.
I would strongly recommend against resorting to Viagra or Cialis at this stage of the game.