I think all heat cycles can vary though the norm is for them to last about 3 weeks. My girl's first cycle lasted 6 weeks. Ugh!!! Her bleeding level varied from light to heavy. She didn't like the diaper either but left it alone for the most part. As for exercise, I took her out ONLY on a long leash did very short throws for her to fetch, played tug and did some hide and seek. You might want to check out Susan Garrett's Crate Games for indoor, brain stimulating activities you can do with her.
Good luck. It will be hard going through two heat cycles, but if this is best for her health, I'd do it.