Why at 45 have I such bad period pain, extremely bloaded tummy and pain seems unresponsive to painkillers.?

Transitions. During our teens & 40's-50's, our hormones transition. Talk with your doc about your transition, possible fibroids, endometriosis & other concerns since the usual things aren't working for you any more. Depending on the cause, there are many different things you can do to feel better soon. How's your diet? Exercise? Good luck.
Try some of these > NSAID’s, SSRI’s, hormone meds, OTC meds containing diuretics, warm bath, heating pad, exercise & acupuncture are excellent for PMS / period. Avoid caffeine, chocolate, alcohol & salt. Get GYN eval to R/O underlying pathology. Consider omega- 3 fatty acids, magnesium (supplementation or through diet) or Black Cohosh with dr ok. Sipping Chamomile can dissipate pain. Ginger helps w nausea.