Problems with dumbbell press

[OverweightMess]

When I first started the dumbbell press I was increasing the amount of weight on it each week. But now I am stuck at 45lbs. At first I thought, its just the muscle has reached a point where it doesn't want to grow anymore. But the strange thing is, I am constantly increasing weight on my dumbbell flies which also works out the chest.

I do dumbbell flies first, but when I am done with them my chest feels tired out.
Could this be the reason I can't press as much as I want? Can you fizzle out on a before workout and be unable to do the workout at full intensity afterward? And if this is the case, is there a way to make sure you won't tire out after the first workout, maybe more carbs before workout or something?

[Kilrov]

Do the more intensive compound exercises first. Don't do flies first, take care of the bench when you start off the routine. No there isn't really a way to prevent getting weaker, you're using your muscles, they'll get weaker as you go further into your workout. If starting with bench doesn't help with the loading of more weight, use the same weight a couple times, before advancing, or microload.

[ele1122]

Do the presses first. This way your pecs can use their full potential. I always finish up with flies to drain the last bit of energy from my pecs.