Could it be a UTI? (urinary tract infection) This happens when bacteria stick to the walls for the uterus and cause an infection. Cranberry helps to stop this. If forms a barrier that stops the bacteria sticking to the lining. You can get it in juice or tablet form. Also, drink plenty of water so you can keep flushing out the bacteria as much as you can. If this is not the problem, I suggest to go see a doctor.