Any idea?

Lauren • In a relationship: 23/09/13❤️ 16 years old💁🏼
It's a bit awkward to say but I don't really poo much, when I do it's only when I'm on my period... I have been on the pill for a while. I've gone through three weeks off it and onto the second box and I'm on my period now so stopped taking them for this week but since I've been on my period I've needed the toilet a lot but it's also very watery and painful to go🙈 
Does anyone have any advice?