What Causes Irregular Periods With Continuous Spotting?

I am 24 years old woman. I have irregular periods. After the completion of every menstrual cycle, it continues to bleed little by little. This goes on till the next menstrual cycle starts. A few days (3-4 days) before the next menstrual cycle starts, the period flow becomes a little more intense. Until last year, I used to get my periods somewhat regular; sometimes with this irregularity. But for the past six months, I am facing this problem almost continuously during all my menstrual cycles. Some elders suggested me to take birth control pills. Some say that taking birth control pills can cause some side effects such as acne, weight gain etc. But I am not sure what is wrong with my body. Please help me. Are there any natural ways to cure this problem.