This is my 5th baby. I've had it with each one and it's gotten worse with each. Try a heating pad but on lower setting... I asked Dr and midwife said it's safe as long as it's not burning hot. Good luck hope you feel better Soon
Stomach muscles or back pain could be related to stretching ligaments and nerve pains due to shifting organs to accommodate your growing uterus. I guess those are icky pregnancy issues that we have to deal with. Try to rest, if possible and relax. Maybe prenatal yoga would help?