help please?

My period is almost 40 days late, which is a little extreme, but it's been a few days late before. I normally get cramps a day before my period, but I've gotten cramps for the last few days with no period. I have realitivly painful cramps, and pain medicine doesn't seem to be helping. I can't be pregnant, and I should be going to the doctor soon but I'm not sure when since my appointment was cancelled. I'm worried I won't be able to get an appointment soon. I have a chance to go to an urgent care center this weekend (my mom is off so she can take me). I don't know if I need to go or just wait it out. Any advice?