I agree that you may be experiencing enough stack that you're actually drawing a lot more than 45 pounds. But you can work around it.

Exercise those muscles with the bow. Hold the bow up at a 45 degree angle and keep it there. Pull it 1/4 back and hold for 5 seconds, back to half and hold for 5 seconds, 3/4 back and hold for 5 seconds, full draw (or as close as you can get right now) and hold for 5 seconds. Then let down the same way. Try to do 10 of those at first. If you can't, just keep going until you can. It won't be long until you can hit full draw with 10 reps. Then up it to 15, then 20. It'll flat wear you out, so be sure to give yourself a day of rest between each workout. If you go shooting one day, skip the workout. When you can't shoot, do the exercise to keep the muscles strong.

I like to keep a heavier bow than I actually shoot so that I can do that exercise.

The first time you draw a bow that doesn't stack at your draw, you'll freak. It'll come back so easy you'll think it's broken and it will shoot a significantly faster arrow. Long draw guys like us are much better off going the custom route.