What Causes Irregular Periods And Pain While Passing Stools During Periods?

Hi, mamy periods were normal then 18 month ago i gave birth to my daughter and ever since then my periods have been irregular and every time it is time for my cycle i get these really horrible pains whenever i need the toilet and sometimes find it impossible to go and as soon as my period as stopped i can go easily again and recently my stomach has blown up almost over night i never thought anything of the irregular periods etc until recently when i got really worried in case it is something serious please help could there something wrong