I need some LSD on my LSD

Bottomline--I am not hitting my long runs. I am at a loss for what is going on. I don't buy the idea that I am ramping up too quick or going out too hard. My training during the week is typically dead on. But that long slow distance on the weekend is killing me physically and mentally. I have already dropped out of the early season marathon to take on a half mary. But now I am concerned about that too. I feel like I should be peaking. And I am....if I want to race a 10k. Here are my last few long runs--

12/8 12 miles 1h 50m HR 146
12/21 13.75 miles 2h 09m HR 149
12/29 12.16 miles 1h 53m HR 149
1/5 12 miles 1h 53m HR 149

Something is not working. I have run out of excuses. I have lost my long run mojo. This is a frustrating time. I think I need to go back to the drawing board and figure out what is happening.