What Causes Intermittent Stomach Pain,leg Pain And Irregular Periods?

I am having stomache pains on my left side off and on. Also my left leg hurts really bad but also it is off and on but i can't walk on it when it hurts and it wakes me up when I am sleeping. I am also having problems with my periods I am having them twice a month and I am on birth control pills. I am having the period on the second and last week of the month. What is going on with my body?