What Causes Clots And Stringy Discharge In Spite Of Taking Pills?

Hi, may I answer your health queries right now ? Please type your query here... i recently started to take the pill as advised by my doctor to prevent painful periods i was told to continue 3 packs one after the other. I am halfway through the second pack and had to take antibiotics. the last week i have started bleeding even though i am dtill taking the pill and today i have been passing alot of clots a few of which have been very large white and stringy with bits of blood on them, though for the most part a creamy colour. I have never had this before what could it be?