This happened to me with Kian, although he was 3 months old & only gained 2 oz in 4 weeks so I was told by my HV to give him formula, which I did (I didn't know much about b'f at the time & just did as she said). I felt terrible too & I also cried because I felt I had failed
I don't think that is a reason to diagnose pnd on its own. It's a normal reaction hun.
How often is he feeding & do you think he's attaching & sucking ok? Do they have a lactation councillor who could visit you? Some mws & hvs don't have much of a clue about b'f.
If you don't want to carry on though hun, there's nothing bad in that. Both Kian & Zac were only breastfed until 3 months which was only half the time I wanted to do it for. If you are happier to formula feed or mix feed then do that. You're his mom after all xxx