Workout and eat healthier. Sometimes it's just genetic and you won't really be able to take care of it. I wouldn't think too much into it - your body is going through a lot of changes right now, all for your baby. Even though you may experience some things that are less than ideal, just know that they can always be addressed after your baby has arrived.
Prenatal yoga is a really good option, too. If you were doing any sort of exercise regularly before your pregnancy, it's normally safe to continue that until you feel uncomfortable doing so. Of course, you should always consult your doctor about exercise first, just to be sure.
You can also do some low-impact lower body workouts that don't require lifting. Think about squats and lunges to get those muscle areas working.
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