I full understand and agree. I once over heard a guy tell his girl friend at the time that she was "broken" because she was on her period and didn't wish to have sex. *grrrrrrrrrrr* (Made me want to break a few things but that discussion is for another thread!)
I basically dislike anything even mildly sexually related during my period. Plus, to be very blunt, sex at that point doesn't really have any sensation for me, especially vaginal penetration and the chances of my orgasming during a cycle are about 1,000 to 1 under the best of circumstances. Plus vaginal penetration, when my cycle is almost over actually seems to set it off again so instead of it being 2 or 3 days it can be a week to 10 days. (So, I like to point out that there is a benefit in waiting just a couple of days normally because it will result in less lost time.)
And that doesn't even get into the fact that my breasts can normally take a fairly strong amount of torture but at that point even leaning against something lightly can cause tears of pain... the cramping... the back ache... the hormones... the memory loss... hell at that point it even seems as though my clit is numb and unattentive. *grrrrrrrr*
So i understand. I basically refuse anything at that point. Or let me state it this way, i prefer not to do anything of a sexual nature at that point and have discussed in detail why and luckily an blessed with Dommes who understand! (One large advantage to serving women... they get it!)
How do we get around it... well, oral or anal is an option. But, my mind/heart isn't even into that normally then either. The best way that i have found to maintain my submission during that time is to take the sexuality out of it and focus on the service. Write something creative, do a little something special, pay extra attention to the other ways that i can be of service. It requires a lot on the partner too though... more understanding and patience. Assigning tasks that work with my period instead of against. Like alone meditation time, quiet baths, personal time. Things that are pampering to me and yet ordered so that 1. I still feel like i am being of service. 2. I am able to get back to full service quicker.
And honestly if they aren't willing to understand and be patient with me during that time then my tolerance for them being "off" when something physical is up with them (be it male or female) is lower. It's all about partnership and managing it in a way that's best for the relationship.