Sounds like you need to do pelvic floor exercises. These can be done anywhere at any time. The muscles you need to build are the ones you use to let go when you urinate. To make sure you are working on the correct ones you begin to pee and then stop mid-stream. (This is only to work out what muscles you need to use - it's not recommended to stop mid-stream all the time!!!) Now that you can do it, do 10 muscle contractions, holding each for about 10 seconds. Repeat this several times a day. Simple. Oh, I believe one added benefit is improvement in your sex life. Double bonus