Remember that it may also be caused by straining to hard to make the mouse move consistently.
This is caused by people turning the dpi too high on gaming mice, which leads to them having to flex/tighten the muscles in their hand leading to pain eventually.
Also make sure your chair has an armrest, and that the height of it matches the desk so that you aren't straining to reach your mouse in any way.
As for the right mouse for you, also consider the type of grip you may be using.
http://www.whatmouse.com/grip-design-explained/
With pain in your hands, you may want to consider getting an ambidextrous mouse. Generally gaming mice aren't like this because people don't play with their non-dominant hand. The reason you want an ambidextrous is so while you are doing other tasks such as browsing through the internet, you can use the other hand allowing your dominant to rest a little while.
As far as exact mice to recommend, I have been using a Razer Deathadder Chroma for a while without issues. I don't know if my hands would be considered "small" though...