DS will often feed frequently throughout the day, depending on what kind of day he's having. It is not unusual to have most days of the week where he'll have about 4-6 feeds during the day, not including morning and night feeds.
I figure that DS is listening to his own instincts about what he needs (be it 'for comfort', nutrition or both), and that the 'habit' is actually just him knowing what works to regulate his appetite or emotional state.
DS rarely has tantrums and when he does have one, he quickly asks for 'Babu' and it's his reset button. The 'habit' stimulates his relaxation responses and he knows it - if he's worked up, one of us soon figures out what he needs and tantrum is averted. I can honestly say we have not had a severe meltdown because Babu is a given for DS. I couldn't care less what anyone else says about 'creating a rod for my back' because one day DS will develop the emotional maturity to find other ways to self-regulate, and by keeping Babu access simple, instead of creating restrictions about it, he is emotionally secure.
It is definitely still my parenting tool at this stage, till he's ready to move on. And when he needs it more during the day, I find it's when I really need more time-out from the daily grind (when I have noticed myself getting worked up about amount of housework, lack of study time, undone errands etc), so it really works both ways.
I don't have PND and I imagine that the other pressures of running a household really impact on your sense of being needed so physically. It's possible that spending a few moments reframing your breastfeeding time with your son to see it as your time out, and time to prioritise emotional security over chores could really help you to view his BFing frequency with more acceptance of and patience for both of your needs