I don’t have much advice, but I thought i’d let you know that I’m in the same boat. I’m 17 too, haven’t gotten my period since February, and 3 tests have been negetive, but i feel like something definatly might be up. Unless I wait for someone to ask me or actually start to show or something,I don’t know how I’m going to find out. Obviously the best thing to do would be to tell someone so I can find out for sure, and start taking the needed precautions, but like you said, it’s so hard to work up enough courage for that,
best of luck <3