I wouldn`t have thought the increase in RAM would cause this. In fact possibly the opposite.
Are you making it work harder - doing more CPU intensive tasks?
Whilst your working, open Task Manager, select Processes and click on the CPU tab until the highest use is shown. This will tell you what is using the CPU most. You should also get a small window in the right hand side of the Taskbar which will indicate CPU use.
You could also download something like Everest Home click here which will allow you to view the CPU temperature and fan speed.