I Can't Get An Erection Anymore

I am 16 years old and haven't been able to get a full erection for about a week now. Before this week everything was just fine. I have tried looking at porn to see if I could get fully hard myself but even this I get only semi hard and then within a few minutes it goes away. Recently, I have tried to have sex with my girlfriend but that did not work either. I don't know what the problem is. I have had sex with her before and everything seemed fine. I am not on drugs or anything and I am very healthy and active. I am thinking about just waiting a week or two to see what happens. I can't get hard myself or from another girl. This just came out of nowhere. Should I be worried about my situation? Should I go see a doctor?