Two Weeks I Had Surgery On My Lower Back Due

Two weeks i had surgery on my lower back due to a prolapsed disc which had hit my nerves so was cut back to my spine to relieve pressure. I am on pill microgynon 30 but since operation have had discharges from my vagina original first week very dark brown almost tar like and now dark purple. I am still taking pill so not making sense. Never experienced spotting before. I am taking tramadol and naproxen