Suggest Remedy For Periods Problem

I have had the implanon implant for the past two years (due to get replaced in November) and haven't had a period, which I think is great but for the past two months I have continuously had a period. The only difference I can think of is that I started taking erythomycin in september '10, and then stopped that about two months ago when I started Lymecycline for my acne, is this what is upsetting my periods? And if so what can I do to fix it? Thanks.