Trying to get pregnant, but my periods have stopped!

I'm 29 years old and have a two and a half year old. I went off the pill in February and had a regular period February, March, and April, then skipped May, then had one in June and now none since. Without birth control I'm normally irregular, occasionally skipping a month here and then. It is unusual for me to skip two months in a row and have never skipped three months! I've taken many pregnancy tests..usually taking one around the time my last period in June came and then every couple weeks. Nothing...always negative. In July, i believe, i was experiencing what i thought could be pregnancy signs- headaches, Very tired all the time, increased hunger, irritability. Those lasted about two or three weeks and went away. I don't feel pregnant..but never did with my first child either. I'm not sure what to do. I'm assuming I'm not pregnant, but not sure how to track my ovulation schedule without having a period as a reference point. Any suggestions?