2 Periods this month?

I sent my OB a message and he said if bleeding persists next month we'll do an ultrasound, but my period started 1/4 and stopped 1/10. i then started bleeding again 1/20, started out spotting, turned into basically a regular period with cramping but not as heavy. it seems to have stopped today, but has anyone had this? we have a 2 year old and 9 month old and i was hoping to conceive again this month...just don't know what this bleeding could be? Breasts are tender, no birth control since september, and haven't breastfed for 5 months.