When my house was built 10 years ago, there apparently was no primer put on the bare drywall before it was painted. I found this out when I had to repair a wall and the paint literally peeled off in sections. I peeled off the paint on this one wall, primed it and used the same paint as the original guys used. What a difference! My question is this. Do I need to strip off all this original paint before repainting a room or can I somehow primer over it so it adheres to the wall better?
Unfortunately priming over the old paint will not improve its adhesion. The primer will simply be on top of the old paint.
At this point you have 2 options; simply apply a coat of paint knowing there might be problems down the road or strip off the old paint. I would try just repainting and see how it works out.