I have stools maybe once or twice a month and it is literally days before my menstrual cycle. and it is not lots that then do come out? where does it all go and what can i do, it causes severe pain, as it feels like i have a blockage or something?

Problem needs fixing: Each person with constipation needs to be sure there is no other disease causing it. If constipation is just due to slow movement of the food and poop through the gut, then the things to try are vegetables, water, fiber with water, prune juice, prunes, polyethylene glycol, Senokot or other senna, milk of magnesia, other laxatives... A doctor can evaluate and consider meds like Linzess.