I am down to 136 pounds. Why do I still have a belly?

I know one thing I have been working @ loosing weight & I currently have lost a total of 44lbs. since Dec 28. I believe you must add the weight lifting this is the same problem I am incurring right now is my belly fat has not gone away not all of it. I was going to try some weightlifting and see if it helped. I ride a total of 24 miles on my bike daily to & from work so I know I am getting the cardio workout but I believe i must add the lifting in order to loose the belly fat along w/sit ups & stomach excercises that might help. I'm only @ 157lbs my goal is to be 120lbs.