Congratulations! I love OB nursing. I hope you will, too. It sounds like you know you are getting into a challenge, and that is the first step here.
I do have a question. Is this a teaching hospital? The residents will do their own exams for the most part. At my facility, we are just starting with residents this year, so we do cervical exams behind them. Some places don't. So I am just curious!
As far as exams on someone with an infection, I have never personally encountered that. However, you're gloved anyway. It doesn't always smell great even if the person does not have an infection. However, smell is part of your nursing assessment. If someone is ruptured, is the fluid malodorous? etc. You get used to everything and anything in OB. Blood, urine, vomit, vaginal fluid. It's all part of the job and you don't notice it after awhile.
If the mother does develop an infection, the doctor will prescribe antibiotics. The main infection I have dealt with in OB is chorioamnionitis.
Psych is everywhere, including OB. We have had our fair share of them. Use therapeutic communication, set clear boundaries, and get help if you need it. We have had to call security before, but it really doesn't get that far very often. It sounds like you have skills in this area, so that is a good start.
As far as CPS goes, the moms will have an idea about that before delivery. They have a clue that CPS will probably be around to do an assessment or take the baby. It isn't a surprise (usually). I have never been in an instance where the mother became violent due to CPS involvement. If there is, there will be extra hands available to help. I'm sure your hospital has a strong social work or case management presence due to the nature of the clients.
I am excited for you! Update us on your next steps or how you feel at your new job.