I think I'll go out on a limb here on this one. I'd guess, that like many others, the draw length of the bow is too long and the draw weight is much more than you can handle.

If you have never shot a bow before then the muscles and the direction those muscles pull are not used to drawing a bow. They can be conditioned (trained), but I would suggest doing so with much less draw weight.

Seriously, I'd get with a good shop and get measured to find out what draw length bow you should shoot. If your Browning can't be adjusted to fit then don't shoot it as there is always the possibility of doing catastrophic and permanent damage to your shoulders.