TTC After Miscarriage..

So we had been trying to baby number two for 8 months. We finally got pregnant last summer and miscarried last August at about 11 weeks. So we’ve been trying again since last August going on almost 9 months of trying. Well I’ve never been late other than the two times I’ve been pregnant. Last month (March) i was 8 days late and then got a 4 day super light period. I normally I’ve always gotten it around the 16th every month like clockwork, and have it for 6 days and it’s medium/heavy. Now this month i was do the 24th and 6 days late and just last night started spotting when i wipe. Also took a test and was negative. Anyone have any idea why I’d be late two different months?