What to do if I am 17 year old guy.2 days ago I noticed weak erections and now I can't even maintain it?

R u 17yo or 39yo? Young men who experience weak erections or erectile dysfunction typically suffer from performance anxiety and perhaps overindulgence in alcohol etc. With time and a supportive & willing partner (not so easy to obtain at 17yo tho perhaps easier at 39yo), ED will resolve the next time around. Older men need to worry about health conditions especially future heart disease. .