This sounds pretty common. Sounds like fluid has gathered around the injection site. Prop can be quite a painful shot, espeially when you are not used to it. There are new guys that want to use prop for their first cycles. Poor guys think prop is a better option because they "dont want water retention", but then they can't get through their cycles without crippling pain.
Anyway, I would suggest injecting slowly with each shot and use larger body parts. If you have other gear that is less painful, you can always mix them and pain will be reduced.
A shot to worry about would be if you were to swell up, feel major pain that gets progressively worse as days go on, starts changing color, deep red, causes fever