Sounds like a good computer to me, only the 4 GB could be the problem.
A notebook always get less good use out of the RAM then a desktop. More and more people with 4 GB are having problems. So did I and I tried everything possible, but in the end I got a better computer...
Doesn't mean you have to too! Besides, the processor, videocard etc sound really good. It would be nice if you could change the RAM to 8 GB.
Else you should make sure that your system is 64 bit and not 32.
Bad cc can be the problem.
Certain mods can ask very much of a computer. Don't forget that mods need to be updated with every patch.
And it's a good idea to turn off the in game store.
Also you can check out the forum better, because there are many threads that can help you, like:
-
What to do if your game slows down-
How much RAM do you have-
Sims 3 stopped working after supernatural download(these are links you can click on)
And there are many, many more tips to find, just check out the
Technical Help board.
I hope this will help you find your way around here.