The biochemistry that gives you such an intense zap with the right person is a limited time offer. Eventually even the most passionate relationship cools somewhat.
Plus you have to consider the physical aspect; five times a day with little sleep? Good gods, I hope you're not using oil-based lubricants because I'd be worried about your junk catching fire. It sounds like you're pushing the physical boundaries quite a bit and eventually the body both gets used to extreme stimulation and just plain gets worn out.
When I was younger (14-16ish) I had a girlfriend and we messed around EVERY chance we got. That translated to maybe 50-80 encounters a week, all with orgasm. After a few months I found that I just plain wasn't working, I'd feel aroused but nothing physical would happen. This was at a point where most guys spend half their day holding a backpack in front of them and I had the opposite problem. When we split, I found my problem went away rather quickly. There is such a thing as too much sex and in my experience, that leads to a lack of performance and interest in sex from the male perspective.
That's why in my current relationships, I actually favor fewer sexual encounters than most because it helps keep things exciting and passionate.
Consider taking a break for a few weeks (physically) and see what happens.
I am as direct as a T-Rex with 'roid rage and about as subtle. It isn't intended to cause upset, I just prefer to talk plain. There are plenty of other people here who do the nice, polite thing much better than I can. I'm what you'd call a "problem dinner guest."