Period or spotting? Period was due 6/1, not sure what is going on!

My period was supposed to start yesterday, 6/1. Since Sunday, 5/29 I've had very light spotting (mostly brown) mostly just when I wipe. Yesterday there was some brown staining of a pantiliner and some red blood only when I wipe. Again, very little red blood. I woke up with terrible cramps on my left side today - so bad I was sure heavy flow would follow, but still very little discharge, and now I'm having no cramps or signs that red blood will come! It's confusing as I'm very regular. I'm ttc and thought I could get a bfp this month. I've had 2 bfns on 5/30 and 6/1. I guess I'm concerned that it could be an ectopic pregnancy, or something else?? I just turned 37 - could this be perimenopause starting? I would appreciate any ideas, thoughts, similar experiences. Thanks in advance!