What Causes Missed Periods Post Birth Control Withdrawal?

Let me preface this by saying I haven t had a period since last October. I m not currently on any birth control but before October I was, in which I had a bad reaction that sent me to the ER. For the past two weeks I ve been having strange symptoms that are raising some questions. My breasts are sore and tender to the touch and until a few days ago they have been a little swollen. I ve had waves of nausea not everyday but most days. I m pretty lethargic and generally lack energy. I constantly need to urinate at least every 2 hours which is not normal for me. I ve taken 3 pregnancy tests within the past couple weeks and all of them have been negative. All of my symptoms seem to be gone except for soreness in my breasts which haven t lessened at all. Never had I had sore breasts for this long.