Breastfeeding my 12 month old with no period. lower abdominal and back cramps, night nausea, painful sex with negative pregnancy test. any help?

Low estrogen state: As long as you are breastfeeding your body will remain in a low estrogen state with minimal pituitary activity. That accounts for the thinning of the vaginal walls and painful intercourse that can be addressed with local estrogen cream or breastfeeding cessation. I also hope contraception is being used as an egg can still "pop out" with attendant pregnancy. See your GYN MD for further advice & Rx.