Why is my MacBook Pro running slow?

Hi,

So I have a 13' MacBook Pro with a total of 4gb ram and 500 gb storage. It has been lagging a bit for awhile now, but not enough to really trouble me. But recently I decided to install Windows 10 through bootcamp and since then it has been hot, slow and glitchy. The only thing I'm using Windows for so far is steam and black ops 3, and the game raises the CPU to 100% and crashes immediately after launching. I realize this system isn't exactly powered for gaming, but it is slow in general and is now failing to run one game with over 100gb of free space on both the Mac and Windows side. I have tried lowering graphics, using system cleaners, and running minimal programs. Any advice?? I have been trying to solve this for the past two days.