I'm Constipated The Last 3 Days And I'm Getting Sharp

I'm constipated the last 3 days and I'm getting sharp pains that last a few seconds but are painful. They come every few minutes. I'm 15 years old and I suffer with bad period pains. I take ponstan for my pain and I went to a doctor before and they told me that after a long time usage of these tablets they can affect me. But I usually get a nausea feeling 3 or more days after my period ends at the end of every month which is usually what I get. But I've experienced this pain and problem the last three days and I have diarrhoea in small amounts but I still can not go go the toilet properly