First, make sure you have the main menu set to 50 as well as in CFM. Also make sure you have accelerated clock turned off and the game length set to 9 or 10 minutes.
Second, IMO the injury setting is critical to gameplay performance. Now, so you got a bunch of injuries early. But at the end of the game, I can almost guarantee you that if your main menu injury slider was set at 50, that most of those injured guys will not be injured headed into the next week. You'll see lots of short duration and game length injuries, but it's not like every guy goes out for 10 weeks. It's not as bad as you think. Stick with it....injuries happen in spades in the NFL; I think this set does a nice job of replicating that given the limitation that we don't have practice injuries and so on.
Finally, make sure to invest in players who have high injury and toughness ratings....that is critical or you're going to get beat up a bit.