Minecraft using excessive memory

My Minecraft has been having excessive lag recently to an extreme so when I checked task manager I see that my memory is at 90% - 97% of nearly 4gb and probably peaking higher (while the cpu is only at 20% - 40% 2.5GHz) causing Excessive lag as low as 20 fps. I have 8gb of installed memory and only have 24 chunk render distance and 8 simulation distance. I wouldn't point to windows since I was playing Halo2A Halo 4 without any hitches.