Time off for MH medication

Hi all, posting this as I'm currently scared about losing my job. I'm on a first written warning for performance, which has deteriorated my MH. It was already bad enough to begin with, but this has pushed me over the edge. (As well as losses of family members).

Because of the MH struggles, I've taken way too much time off work. I've been told one more sickness absence and I'm going on formal attendance management. This was due to self certifying for a week as my anxiety was very bad, was given medication and I returned a week later (on the advice from the doctor).

Now, I'm planning on speaking to the doctors about additional medication but I'm scared that the side effects will impact with goals I have for the PIP. I'm just scared my manager will use this as an excuse to get me dismissed.

I really don't want to be dismissed, but it's cared my mental health is putting me in a position where this will happen? Am I just overthinking this?

Before anyone else asks I've had 2 OH assesments, so i doubt that having anymore would help. One was followed through and the other one wasn't.

I'm just scared it'll be they come out and day they've done everything they can, but nothing has changed and I'll be let go.