My Periods Always Come On Time, I Was Supposed To

My periods always come on time, I was supposed to get my period June 10, but I only received discharge on the 11th that was slightly pink; this only happened the one time. I was then supposed to receive my period July 8, but I have not yet received it, no discharge or anything to indicate it would be coming. Today I had pale yellow discharge with no odour. I have taken 4 Pregnancy Tests since June 13, the most recent being July 12 and all have come out negative.
In the past month I've experienced extreme fatigue, and some nausea.
I am 25 and sexually active with my boyfriend of 2 years.
Any idea what could be up would be helpful!