If i go in a plank position my body spasms and if i do a sit up my lower back spasms been like this for years now getting lower back pain neck pain?

See a doctor: You may want to see a doctor and get your electrolytes checked. Especially if this is getting worse.

Yoga shouldn't: cause pain. If you're having pain while doing Yoga, then one of three things is going on. Either you're not doing the posture correctly, you're doing a posture your body's not ready for, or you have a musculoskeletal problem. Normally I'd say just to find an experienced Yoga teacher, but, since this has been going on for years, it's time to see a doctor. Best wishes. Dr. Anne