Breakthrough bleeding or period?

My last period was on Jan 13 so it's been 2 months..no period. I have been having many pregnancy symptoms...frequent urination, headaches, tired, nausea, weight gain of about 6 pounds all in my stomach. I have had multiple neg test at home and 2 neg urine tests at the dr. They did a blood test 2 weeks ago and it was neg too. I am scheduled for a pelvic ultrasound on Wed to finally (hopefully) get a definite answer. Yesterday i had some light spotting only on the tissue twice...once in the afternoon that was light red and once last night that was very light pink (totally different than my period looks) It hasn't happened since. It would have been the time of the month to start my period. I have been reading about breakthrough bleeding and read that it sometimes happens around the time that you are supposed to start and often happens if your hormones are low..which would explain the neg tests. My question is has anybody else experienced anything like this? I feel pregnant. I have three children so i know what being pregnant feels like i just can't get the test results to prove it. Has anyone else been pregnant but the test results were negative? Does the spotting sound like breakthrough bleeding? Any help or advice is greatly appreciated! Thanks!