What Causes Repeated Miscarriages After Withdrawal From BC Pills?

hi, i am 25 years old and have a 7 year old daughter. i came off the pill in september last year and fell preg about a month later then had a miscarriage in december and another in june. im really worried that theres something wrong with me. i had an ultra sound done and all was normal. i have very irregular periods like an average of 42 day cycles and very light pinkish kind of bleeding