period twice in one month??

I had my period at the beginning of the month the 5-9, me and my husband have been sexually active and I haven't been taking my birth control like I should. Anyway, I got my "period" for the second time in a month, the 24-29. Has anyone else experienced this? What would be the reason for this??
*I have not took my BC in about 3 months, I had an allergic reaction to it. I've tried 3 pills and the shots and a severe reaction to all.*