LTH - I think it is (in this case) all or mostly in your head, honestly....and maybe this is the reason why. I may be talking rubbish, but hear me out
This time round, could it be you think of yourself as a breastfeeding mother? Sometime in this last pregnancy or shortly after birth, you bought the breastfeeding ticket. Maybe this was because of stuff you had read, people you had met, whatever.....maybe it was because you were a bit older this time with baby No. 4 and just had a different outlook and attitude to this as well as other things.
Now, it didn't go well. But you still have that ticket in your pocket. It reminds you of how you thought of yourself, and how you would still like to think of yourself, in a way that touches you more deeply than it did before with the other children (maybe this is your last baby...that would make a difference, too).
So could it be that what we have here is regret and sadness? Yes, it's alongside all the positive stuff of keeping the challenge of ebm going despite everything, and feeling good that the baby is getting the goodness of it...but it's still a raw spot, and it makes you hear 'mafia' when 2 mothers come up and say something a little bit silly but not cruel, and it makes you see hostility in people's silence and people's glances.
You're still hanging on to that breastfeeding ticket and that's great. It's how you see yourself, but with a bottle in your hand you know that's not how the world will see you. So you feel embarrassed, and awkward, and you feel a compulsion to explain. So where does the pressure come from? Inside?
What do you think?