Substituting

In franchise, for some reason my players keep auto subbing after only 3 or 4 snaps. I have my 4th string receiver and 5th string receiver replacing 2 of my receivers, my backup tight end is constantly replacing my starting tight end, same thing with my backup running back. My starters won't come back into the game unless i manually do it. I'm not sure if this is a fatigue or not thing since ive also noticed that my opponents running backs always start the game tired and they get subbed out for their backup running back for the rest of the game.