Late Period!

My last period was in early April. The one before that was in early December. So now I'm 50 days late. I do have sex but it's protected and I'm only 16 so I can't just go go the doctor without my mom finding out. Before my last period started I took about 6 pregnancy tests and they were all negative. I haven't taken any this time because I feel like it's a waste of money. Now I'm having really bad cramps and just feel bad all the time. What should I do?