Okay so I don't really know the the year where it came out but I watched around 2004-2005. Its story is pretty general with a tentacle god guy so I'll describe some scenes.
It starts inside a temple where a couple are having sex and there's like a canal for semen collection.
Somewhere in the middle of the movie, there's a scene where a group yoga/gym session gets tentacle raped after the instructor's stomach burst open with a tentacle monster.

Please help! I've been looking for this for a long time now.