How are you placing the strap over your neck - that may be the problem ??

If you're a right-handed player the strap should come off the heel (or neck) of the guitar, over your left shoulder, down your back to your right side and under your right arm to the end pin in the lower bout of the guitar.

I've seen some people (including a girl mando player in our band) just plop the strap over their neck so it comes off both shoulders. This puts a lot of pressure on your neck, is uncomfortable for the right hand, and looks really dorky besides !