well , any mod which was not coded by a good coder will cause you lots of memory issues.
also, there is a really good mods created by great coders (I don't wanna mention names nor mods) , yet the way they function is using lots of resources although they are fully optimized mods.
try to turn on the debug mode , and keep an eye on the memory usage below.
start turning off mods one by one , until you figure out which one is causing all of these troubles to you.
cheers !