Scared!

Hi! I'm a 21 year old that has always had issues with my period. I recently found out that I have thyroiditis. The first dosage did not lower my levels, so this past month, we have increased it. I also started a new medication for migraines. I've lost 10 pounds this month and have been under a lot of stress. 
I didn't have full on sex this month or past months, but there was an instance where this guy and I were making out and he stuck the head in. It happened twice, but then, we stopped. This was at the beginning of this month's cycle. 
My period usually starts one month and one week from the date of the start of the last one. My period was supposed to start on Saturday, but now it's almost Wednesday and it hasn't. 
I've been having a lot of cystic acne breakouts, slight bleeding for 1 day that looks like old blood when I put a tampon in, sore and tender nipples (which is very usual for my period), some cramps (which I always get horrible ones when my period starts), and very tired. 
I took a pregnancy test on Sunday and it was negative, but my period still hasn't came. I don't know why I haven't gotten it, but I'm really nervous. Does anyone have any ideas? I have another test I'm going to try tonight, but for the time being.