Are They In Pain,& What Medicine Do I Use If So?

Female dogs should be sterilized to prevent ovarian cysts and cancer, not to mention complications from pregnancy, assuming you don't wish to use her as breeding stock.
How old is your dog, and how long has she been in heat?  Normally, a dog in heat is quite active and doesn't lay around.  That could indicate a problem.  If she's not a biter, you should gently lift her lip up and inspect her gums.  The gums should be a nice pink color, not pale or yellow.  On some dogs, this is hard to tell because the inside of their mouth is black, however, you should be able to find a flesh colored spot to inspect.  If this area is pale, yellow, or otherwise discolored, it could be an indication of toxic shock, and you should take her to a vet immediately.
You should check to see whether or not she is dehydrated.  This can be easily done by pulling on the scruff of the neck, making a tent of the skin, perhaps an inch high, and releasing it.  Even on wrinkly dogs, such as a Sharpey, the skin should pop back immediately.  If it doesn't, this indicates that your dog is likely dehydrated and should be taken to a vet.
How long has she been having diarrhea?  It is not uncommon for dogs in heat to have diarrhea, but that is usually associated with pregnancy.

They get cramps and such just like us. Unfortunately she is just going to be a little crabby and tired. The runs is pretty normal, just make sure she gets a lot of water. Try walking her more than normal or longer to help with the cramps. I know my girl is a real baby when she is on. Baths help too.