18 year old with small penis

As far as having a small penis when you're flaccid.... i mean, theres not much you can do about that... I'm in a similar boat where mines only like 2.5 in when soft... and like roughly 6 inches erect. If you're worried about girls, guys, whatever you're into,like  laughing at you, i would recommend you dont worry about that. Because if they're seeing your junk, you're likely getting intimate with them, and once you get hard, thats all that matters, and 6 inches erect is average and nothing to be ashamed of. I should know, my girlfriend is perfectly "Satisfied" with my size haha. If you're embarassed about having other guys see your flaccid penis like when you're in a locker room or other setting when you have to undress, just try to keep yourself covered as much as you can down there, or even shower in your boxers if you're in a community shower... thats what some of my football teammates did back in HS... 

As far as one testicle looking more descended than the other... that may or may not be a bad thing. I dont want to alarm you, because i honestly was worried about the same thing when i was like 14 or 15 and i told my dad, and he said sometimes thats just how your testicles hang, with one looking more descended than the other. Another reason for why your testicles might look more descended at some times than at others could be the temparture that ur testicles are in. If its cold, your testicles sometimes shrivel up towards your body, and they might look kind of small. If its warm, your testicles would do the opposite and hang lower. I dont know for sure about the warm temp making em hang lower tho... i do know that the one testicle hanging lower than the other usually is just a physical difference in guys, just like penis size... sometimes ppl will vary in size and shape.... etc....

As far as testosterone levels being low, you havent been smoking pot right? Because mine have been lowered slightly due to pot smoking... Well whatever the case, it could be a variety of things that are causing you to have low testosterone levels... Diet, certain medications you might be on, i dunno, whatever it s you would want to probly check with your primary care doctor, or your parents, or if you don't feel like seeking out either of those, you could always go to.... 

I hoope that clears some things up for you, and if you have any more questions, I would be happy to answer, but if not i hope you find what you're wanting or looking for, dude!

Btw, i am only 20, but i do know a little bit about these kinds of things... we guys have to deal with some type of penis and/or testicle related worries at some point, i just found out the answers to my worries when i was a bit younger. S'all good though, everyone's different in their experiences.