Getting flippant with flips

Megumi and I have decided to improve our hiyaku ukemi (flying forward flips), so we've been doing a few flips this week after class. My right side flip is getting a little better, but I can't say I'm seeing any improvement yet on the left side. Then yesterday, we did a lot of hiyaku ukemi in class and of course, a few times I landed poorly and jarred my lower back. When I woke up before class today, I felt a bit sore. Not a good sign. Could it be that my form is actually getting worse?

Today we did a few different ikkajo nage and one kotegaeshi technique. R Sensei had us focusing on fluid movements, but I didn't feel very spry today. I was a bit slow and stiff, and halfway through the class, I felt like I was out of gas. Hopefully there's no flipping in tomorrow's class. My body needs a break.