What Could Cause Menstrual Irregularity?

Hello. 26 year old female attorney, 5 7, 167 pounds. I had protected sex in early June, then missed my June and July periods and have not had my August period yet. I did two over-the-counter pregnancy tests; both were negative. Traditionally, I miss one period every year. I ve been experiencing ovulation pains on both sides, my breasts are sore, I have pain in the lower back which radiates down the left leg, and within the past couple of days I ve experienced sharp, burning pains when I take deep breaths. No morning sickness, no weight gain or loss. My mother and grandmother had hysterectomies in their 30s due to benign tumors; grandmother is a colon cancer survivor. My doctor can t see me until September. Any advice is much appreciated.