You should never wean before 4 months (17 weeks). Continue to breastfeed on demand or to give your baby the usual amount of infant formula milk (at least 600ml.
Eating foods that decrease inflammation in the body will help to tame menstrual cramps. These foods include fruits, vegetables, whole grains, legumes, nuts.
Try and distance yourself from her affair and see things objectively, or from the big picture. If you DO still love and believe in your wife, then it's probably.