Have to say I'm with Kali - there is not a very good way to say over the net whether or not the bike fits you, but a 50 does sound a bit large for someone who is 5'3" - now if you are long in the arm and torso, then that may well be quite right for you and some manufacturers measure differently, but your discomforts do sound a bit like an overy long top tube.

Do you feel stretched out, can you reach the handlebars/brakes/shifters comfortably while leaving a bend in your elbows - if your arms are straight out, elbows locked, thats a pretty good sign the frame may be too long.

Can you have someone take a photo of you sitting on the bike? (side view)