Hi, i'm so sorry you have worries about this again, the fear of what might be is itself very stressful.
But do remember, this time things are a little different. You've had a pregnancy before so you know that there is the potential for hormones to knock you off balance, and you'll be able to see it coming and help yourself better than last time. That makes a huge difference
Remember that you are not your thoughts, that pregnancy is quite an extreme experience for our body and mind and that it is only for a finite time of a few months. This is not forever.
Do you have a talking therapist? As previous poster mentioned, a GP should prioritise you but if you want to take things into your own hands, a lot of areas have therapists who provide low-cost support on a self-referral basis. You'll just need to do a little googling and send some emails, and someone will point you in the right direction.
A friend of mine who has mental health issues was supported brilliantly by her GP, who continued to provide her medication throughout her pregnancy, which kept things stable for her. So medication might be a possibility too.
Half the battle is identifying you might have problems and openly seeking help, so you are doing really well x