This is normal. What you may need to do is do Kegal (sp) exercises to tighten up the sphincter muscles to help prevent this. In the last trimester.....you probably found yourself going quite often as the weight and position of the baby pushed against the bladder/urinary tract. Why pelvic and Kegal (sphincter) muscle exercises are recommended after birth.
You shouldn't have to urinate all the time now. You may have an infection that will make you go every minute it seems. Get it checked for your convience. What Laurie said about Kegals will help control and tighten the mucles if they are weak after having a baby. But it sounds more like your just have to go all the time not control.. Not sure but get it checked by your obgyn.