Diazepam is the generic name for Valium. It is used as a muscle relaxant and for anxiety. Motrin is an over-the-counter form of ibuprofen used as a pain reliever and antiinflammatory. It helps reduce pain and cramping associated with the menstrual cycle. It does this by blocking the action of a substance called prostaglandin.
Prostaglandins have many functions. One of these is to make smooth muscles contract. During the menstrual cycle these contractions helps empty the uterus of any blood when there isn't a fertilized egg. Blocking this action also keeps skeletal muscle from contracting and promotes relaxation.
It's never a good idea to take more than one drug at a time without checking with your pharmacist or doctor first. Drug interactions can have serious side effects.