What the heck is wrong with my cycle!

My period has always been like clock work, I stopped the pill in early December and my cycle regulated pretty quickly (i was on a very low dose BC). My period in January was about a week late due to some extreme weight loss I had and probably a bit to do with stopping my pills, but this isn't the first time it's happened but it doesn't usually affect my cycles as long as I get my body fat back up rapidly. Once it started my period was pretty normal for me, I put some weight back on my body and 28 days later my period for February began on the 9th (right when glow said it would be). I'm now roughly 16dpo for this cycle and af is 3 days late . I don't use opks or temps to track ovulation, just go off any cramping, CM and my CP. Glow said I was ovulating the 24th but I think it may have happened in the late afternoon on the 23th. Timed our bding just right :) I thought for sure this was our month and I was definitely feeling confident when af was late on the 10th but here's the thing, I'm still testing negative! I'm using test strips from Amazon that are supposed to detect hcg levels as low as 25 (I know they aren't always as accurate as they say) but there's only one line coming up everytime, I also tested negative 3 days ago with a frer :( I had some pretty moderate cramping on Tuesday night and it radiated into the left side of my back, the uterine cramping lasted about 4 hours but the lower back pain bothered me into the night a bit and my hips were sooo sore, I couldn't sleep without a pillow between my legs. but by morning I was fine and I've had nothing since other than some very mild cramping the past couple days. My periods are usually pretty painful (I thought I was being crazy until I finally confided in my mother, who has very similar periods to me, about how bad the pain was and she said her cramps get as bad as labour pains and that she totally understands) and my flow is very heavy, I can tell af is coming because a week before I'm due I cry at everythinngg and my pain is usually a 12/10. but I feel pretty normal as far as mood swings go and like I said my cramps have been very mild and they feel different than usual. Does anyone have any advice to offer? I don't know if I should bother to keep testing or if my period is just being weird for the first time almost ever