Wow, those modelling ideas are great, I never would have thought of that. It's true that you do not need to be in "model" shape to get jobs, either, especially when it's pregnancy jobs.
I was going to suggest a serving job (waitress) because indeed, it's one of the highest paid jobs in our area and definitely the highest as far as part time jobs go.
Since you are pregnant, it might be easier for you to get a retail job, perhaps in a maternity store, or even at a grocery store as a cashier (if your area utilizes unions, if not, then the pay might not be worth it.
It might seem simple but some people overlook simply checking in their newspapers every day or job ads. I have found some really cool opportunities just reading the classified online (for our local newspaper) that other people couldn't believe I had found.
If you are in a group of any kind, I'd suggest you spread the word, perhaps by email, that you are looking or a p/t weekend job and see if anyone has any leads for you. Good luck!