Early Period and Taking Progesterone

We are trying to get pregnant. My period never comes earlier than 28 days (only occassionally on day 29). I'm taking progesterone (orally) after ovulation and folate, folic acid and aspirin all month b/c I am homozygous for mthfr. I started bleeding on day 26. It was two or three days of just spotting followed by a bit heavier flow tapering off to spotting again. Here I am 10 days into it with still a bit of spotting. My period is usually 3 days long and very much the same every month. Negative urine pg test on day 27. Very weird. Any thoughts about what might be going on?