Leaking liquid stool in panties...?

I'm a teenager so It's a bit embarrassing but I always have liquid stool in my underwear, it's disgusting and I have been constipated for a few months now. I might also have IBS. My doctor said my large intestine is enlarged from being constipated so long, once I take this medicine will it go away? Also, how do I control this? I have it in like all my underwear and its disgusting.