Natural cycle symptoms and conditions

I have been on Yasmin for three months now. I just finished my third pack, actually on the placebo week. The first month I had no symptoms or reaction to the pills and I got my period the first day of the placebo week. The second month I had unprotected sex and began to have cramping, lower back ached, nauseated, frequent urination, and at the end of my second pack I did not get my period. On my third month, much of the same symptoms and now I am two days into my placebo week and am worried I might be pregnant. I have taken the pills religiously and have not missed a pill. Please let me know if anyone has had any of these same symptoms and possibly missing two periods in a row! Thank You in advance.

I have been taking the shot for nearly 4 years and the only side effect I have ever experiences is loss of my period, and frankly it has been wonderful not having to deal with that every month.