I think about STIs and sexual health as a risk awareness and management problem. How much risk is acceptable for me? What consequences am I willing to live with? What consequences am I not? What is a catastrophic event I want to avoid at all costs? So, for example, for me I am fine having unprotected oral sex with partners (who've been tested and have an awareness of their risk levels too) because I've already been exposed to the STIs most likely to transmit via touch (HPV and HSV (cold sores in my case). I would prefer not to get HSV-2 but it's a risk I'm willing to take by not having barriers with oral sex. I've gotten vaccinations for Hepatitis A and B to minimize my risk of getting those diseases which can have very serious health implications - and I do not do unprotected blood play or penetration. These are the sort of decisions I've made based on what level of risk I'm willing to take.
So mulling over your situation, it seems to me that wanting to get pregnant and having medical conditions that can impact fertility really ups the level of risk you may be unwilling to deal with. Several STIs can badly hamper or even destroy fertility in women. You may want to seriously consider stopping intercourse with other partners besides the person you want to be the father. And you may want to consider stopping having sex entirely with other people until you conceive. Another option would be to re-conceptualize sex away from intercourse/penetration/genital contact for those partners who are not going to be genetic contributors. (Sorry, awkward phrasing! I don't know the genders of your partners.) This would reduce but not eliminate your risk.
The thing is though, if you go this route, you would still face a serious (in my opinion - yours may vary!) risk of harm from STIs if your 'genetic contributor' partner (again sorry for the awkward) continues having penetrative, genital contact sex with their other partners. It would help, yes. However, women are at much greater risk of infection from male partners than the other way around. Physically it is easier to transmit being penetrated than the one doing the penetrating. So if you decide to not having sex with your other partners until you conceive, from a risk reduction viewpoint, it would be ideal to have your partner also refrain from having penetrative sex with others as well. This is not an easy or small thing to ask. And it sounds like both of you have other partners currently. But you have the right to ask. And assuming he is willing, you both will need to think about if this takes some time (and I hope it does not), how to handle that. Talk with your doctor openly about your other partners - this is crucial information they need to know to truly give you appropriate advice about pregnancy, fertility and so on.
Talk with your main partner about the level of risk he is willing to expose you to. That's the critical question if you decide to not have penetrative sex with others while trying to conceive. Have that critical conversation about the levels of risk you both are willing to take, for your own body and mind, and for each other and your children. For example, you may be ok with getting herpes because the consequences are generally not serious for adults. But children exposed during childbirth to herpes can suffer serious health issues or even die. This is the kind of thing you two need to talk about. And for the best protection of you both, it's not a decision you should make individually. You can, of course. But it's not ideal.
Also, while I think I personally would tend towards closing the sexual relationship to the genetic contributors until conception and birth, don't think this is an absolute, you must go this route. It's not. It's the risks and consequences you and your partner are willing, or unwilling, to bear.
Also, people who want to be around you, who love you, who want the best for you, will wait for you to conceive and bear children. If they don't want to wait, that's their prerogative but put yourself, your partner and potential to be parents first.
I wish you the best!