I'm on the pill, is it bad to skip periods? i get bad sciatica each month when i have a period. also is getting a blood clot when not menstruating bad

No: No harm has been associated with using medication to suppress periods for up to one year. That being said, most women find that to be a strange concept, so these forms of birth control are often formulated to permit menstruation once every 3 to 6 months. Getting a clot in a vein or artery is always bad, but period clots if that's what you mean are normal and very common.