Hi, I'm A 25 Year Old Female. I Have Four

Hi, I'm a 25 year old female. I have four children and I had my tubes tied after my last one a little over a year ago. I had some spotting on the 12th of last month (March) and have not had a period at all this month. Also, the 12th was later than I ever have my period so that concerned me as well. I'm having pregnancy symptoms and I have taken a home pregnancy test twice but both results were negative. I've looked up the symptoms of ectopic pregnancies and don't have any of those either so I'm really confused as to what's going on. Especially since the two tests I took were negative (1 today and 1 yesterday). Even if my period were to continue, I would be almost two months late as of now. Do you know, by any chance, what could possibly be going on? This is driving me crazy!