PLEASE HELP :(

I always have a very regular cycle- 28 days to the MINUTE every month. Well on my last cycle, I didn't get AF until I was 2 weeks late-it was super heavy and just had clots after clots after clots and it was so bad. All my tests-including blood-were negative. Now still TTC, glow changed my cycle to a 35 day cycle but another app I use says I still have a 28 day cycle-that app says AF due 9/28 but glow day 10/5. Which one do I listen to? Anyone have this happen to them? BD every other day during both apps fertile windows though and on the peak day. Had some light spotting a few days ago for 2 days-light pink and light brown. Anyone have this happen to them? Please help