Hi Mars,
it's a common problem. And people who do lots of bench can also be prone to injure it when they go to fatigue/muscle failure because the stabilizing serratus fails. You know which athletes really don't have a problem with their serratus? Boxers.
They need to have good reach with their punch and be able to have their shoulder stable for their punch......
What you probably need to work on is protracting (bringing forward) your shoulder when doing push ups. In other words, "Push up, Plus".
At the top of your pushup, push your torso even higher by making your shoulders go forward.
Serratus is a scapula stabilizer so endurance training for this muscle, rather than pushing lots of weight with it is key. same with postural spinal muscles.
If after working on it, you feel that you're still not getting results, consult your local chiropractor, as nerve entrapments can also affect this area as well.
good luck