Paint Gun Help

I am having some problems lately with my HVLP gun. It is a Devilbiss Starting Line gun using a 1.3 tip and 20-25 psi inlet pressure, spraying PPG Omni primer. I have used this gun numerous times with no issues and all of a sudden, the last 2 or 3 times I have used it, it has caused me some problems. What is happening is that paint is dripping out of the gun tip after I put the paint in the cup without any pressure on the trigger at all. I have had it in a holder while pouring the paint in and it has run out all over the floor. I have had to screw the flow needle pretty much all the way in until I get near the object to be painted. I believe the gun is clean (I haven't done anything differently from when it worked flawlessly). I cannot find anything that would cause the problem. I religiously clean the gun up immediately after use every time I use it. I have no idea where to start. Anyone have any ideas? Thanks in advance. L8r

Jim