More detail would help, but let's assume you run 6:30 pace for a 5K race. Your easy pace in the Tinman calculator, then, goes to 9:30/mile, and you can only muster 12:30 pace on your easy runs.
My hunch is that you are in quite poor aerobic condition now and you are running more volume than you can handle. I suggest cutting back your mileage and maybe taking an extra day off until you are able to run your easy days at or near Tinman's "very slow" recovery pace without straining.
Feel free to run a mile or two warm up and down at 12:30 pace. And be sure to adjust for conditions and terrain. You don't have to run 10:30 pace in full sweats or on hilly routes.