In a nut shell here is what I am 100% positive about your situation.

You bought a bow that has too much draw weight for you. Period!!!!! Now whether you chose this on your own or with the advice of another, you got too much bow.

This happens to a pretty large segment of people who bowhunt. They don't know any better and usually are younger people with a higher level of testosterone than us older guys. Don't feel too bad about it. It's almost the norm. Testosterone gets in our brain and jiggles our ego around, forcing us to throw common sense out the window.

Lack of experience is part of it, too. We THINK we are stronger than we really are. Bigger is better. More draw weight is better. 70# kills better than 60#, etc, etc, etc. Peer pressure, maybe?

Some might disagree with me, but I honestly think you should see about gettting lighter limbsfor your present bow or trade for another or whatever options your dealer might allow you. I think you should get a bow with a weight range 10# less than what you have now. In other words, if you have a 70#er then get 60#.

You can develop the muscles for drawing and holding a bow, but you have to be able to shoot the bow repetitively to do so. You should be able to draw and aim no less than 50 times before you start to feel some fatigue. That's how your muscles will develop memory which will eventually lead to more strength. However, you may never be able to shoot 70# so don't be ashamed of such. Archery or bowhunting is a sport of accuracy, not brute strength. At present you may be on your way to shoulder injuries which could ruin your archery career before it gets off the ground.