Naenae,

Heat can be really good for loosening up tight muscles and relieves pain associated with AF cramps a lot too. Have you got a heat wheat bag or a hot water bottle?

As far as exercise goes, the walking sounds great. Have you also got a swiss ball? If you do, you can do some swiss ball stretching and light exercise using that.

Have you tried a hot shower even?

I think that if it doesn't get better, you may be better going to see your doctor to check all is well in there.