Hi I'm a 19 year old boy and I don't get a arection that good it does not stand up my sex life is not good why I can't get it up and I'm only 19?

Get it checked.. As a young man, you should be at your prime at this age and your discription is a bit unusual. Do you get nocturnal erection? I.E while you sleep and early morning erection? If yes, then it is working and you may have a mental block somewhere preventing u from getting one while u are aware of it. If no nocturnal erection etc..I would see a doc for some evaulation/testing....Good luck.