I don't know if I"m putting pressure on the wrong part of my bag, but when ever I have a lot of piping to do, I get horrible hand cramps. Is this normal? If not, how can I avoid it? Is my buttercream still to thick? I added so more much liquid than the recipe(s) recommend and still am getting hand cramps. Ouch!

It isn't normal to get horrible hand cramps.  Some ideas...take a break every 15 minutes or so and stretch your hands and fingers, do a little piping every day (with some practice icing) to build up your strength and endurance.  Try using a different bag, maybe the fabric bag would be easier than a disposable type bag or vice versa.  What size bag are you using?  I see some decorators using a huge bag and then they just use a small pouch of icing that they are actually working with, so maybe loading more or less icing in the bag?  And most importantly the thickness of your icing.  It should be just thick enough that it holds its shape without drooping.  It shouldn't take a lot of pressure to get the icing out of the bag.  I would play around with some and just keep adding more liquid, pipe with it, add more liquid, pipe with it, etc and see how soft it can get and still keep its shape and how that is on your hand.  Instead of adding more liquid you can cut back on some of the powdered sugar also.  Just some ideas to consider. 

yeah, i agree, try a smaller bag. it shouldn't take so much pressure to get the frosting out that it cramps up your hand.