I would try another one. They are very fussy things. Last one I put in gave up the ghost almost immediately, and it is by no means inconceivable you got a dud.
Get your oil pickup cleaned too, because it was a blocked oil pickup that set mine off last time around. Sump off for that. There are excellent instructions in the how-to if you do things yourself. Don't listen to the griping about the difficulty, because it is pretty easy and straightforward. It will only cost you a few bucks for a tube of silicone gasket.
The switch never came good after pickup cleaning with mine. Even though it was near brand new before, I had to replace it.
If not that, the oil pump might be giving out. You have oil pressure issues. I guess you changed the filter when you changed your oil, so that is good.
Are there any noises coming from the engine?
