What could be wrong?

About a 1 1/2 months ago car started stalling on me. It would do it mainly in idle/when I go from drive to reverse. Stalled once while driving on the road. It did have a trouble starting back up but with a few revs it turned over. I tried something simple to see if it would work used a fuel injector treatment. For a month with 2 treatments it worked no problem. Now a couple days ago it stalled when I was idle in drive and put it in reverse then started it back up ok. That next day I get in my car after work and it wasn't starting. Tried it again it hesitated to turn over but started. I let it sit overnight went out this morning started up ok. I shut it off tried again it was fine. I let it run for 5 minutes while I checked fluids (all fine) turned it off. Tried starting it again and it was hesitating. My oil gauge also has been going crazy. I was told I had a minor oil leak when I changed my oil last. I had it checked when everything first started happening was told nothing was wrong. Please if anyone can help me figure out what is wrong it would be very much appreciated!