Pregnant?

I was recently taking depo shots but I stopped about 4.5 months ago. I had a light period last month at the beginning. According to this app I should have started my period 5 days ago, but I haven’t. I noticed some spotting at the beginning of the month. However I’ve taken about 6 pregnancy test since the first day of my missed period and they all say negative. I’ve felt a little off. But if I’m not pregnant then why have I been feeling symptoms?