I have no pc muscles on one side.
Again, a question for your doctor with the aid of an MRI. I don't know, partly because it's hard to say if what you are feeling is what you assume it to be. It would be hard for a even a medically-trained person to diagnose musculature with a finger up the vagina; there is a risk that you are feeling something normal and assuming something about it. Have a good medical workup including MRI, and see where that takes you.
Well does this mean one day I'll be loose because of the lack of muscles there? Is this common?
That's a question for your doctor, but I would bet not. Prolapse is more often caused by having a large number of children. (The uterus is not just held in the body by the muscles of the vagina.) When you get a good ob-gyn that has resources, ask if he will order an MRI of the abdomen with attention to that area, and see what the actual musculature looks like.