Re: lag since downloading cats and dogs expansion pack.
@chellogs2016 Your dxdiag shows a number of issues that could be causing the lag you're seeing. You're correct in guessing that your laptop is not powerful enough to run Cats & Dogs properly: its processor and graphics chip are both below the recommended specs, and 4 GB RAM is technically enough for the base game but usually not for the base game plus a number of packs. Aside from possibly adding more RAM (I'd have to check whether this is doable), the components are not upgradable.
A more immediate issue is that your hard drive has only 6 GB free storage. That's not nearly enough room for Windows to maneuver properly. Under normal circumstances, 20 GB free would be ideal, and 15 would be enough to make sure the free space wasn't causing any problems. However, given how small your hard drive is, it might not be possible to clear enough space. Deleting Cats & Dogs couldn't hurt though.
Additionally, the dxdiag lists a few system errors having to do with an unspecified driver. It's not clear whether this has anything to do with Sims 4, and clearing more space on your hard drive could help regardless. But it's worth looking into if more free storage doesn't help.
Ultimately though, there may not be a good approach to playing on this computer, especially with C&D installed. Even with the other issues addressed, the hardware still won't be able to keep up.