I really would not worry too much. Yes, biopsy and cancer are scary words. Believe me, I have been through them both and lived to tell about it.
You are 21 and still going through hormonal changes that really do not level out until about age 25 for the average woman. Then a few more years down the road we experience more hormonal changes. It can suck being a woman sometimes.
Anyway, there are times in our lives when our periods are not textbook or picture perfect.
You made love with your husband in the month of June when he ejaculated, and then went on to have a normal period the first week of August.
This tells me that you are most likely experiencing a symptom of the ASCUS, or just an irregular period. We all have had irregular periods before. Really nothing to concern yourself with now.
Also, have you been under any stress lately that is in excess of what you normally experience? This can lead to irregular cycles also.