Welcome to the forum!
We've had a few moms here over the years who've had abscesses and biopsies, various surgical procedures on the breast- and I think that most of them have been able to nurse during the immediate post-op period. As long as the incision is not right where the baby's mouth falls, the moms have been able to keep a bandage over the incision and just nurse. I would search the forum for threads on abscess, bipsies, etc., and see what pops up.
Formula can be hard on a baby's tummy, and can cause discomfort and sometimes constipation. The good news is that if your baby is pooping every time he eats, he is not constipated. Maybe a little uncomfortable, but not constipated. You don't want to suspect constipation in a breastfed baby unless the baby is going >7 days without pooping and the poop is hard and pellet-like- almost like rabbit poop- when it is produced.
So let's talk about that lump on the right. You definitely want to work on draining it. So you want to nurse on that side as much as you can. Vary your nursing position to ensure that all areas of the breast receive drainage. Try to massage the lump with your hand, and also use moist heat on the breast and on the nipple, and try massaging the area with some sort of vibration- an electric toothbrush would be good.
Since I am sure you are on antibiotics right now, I also strongly suggest taking a good probiotic and practicing good breast hygeine- change your bras, shirts, and towels daily and wash them on hot. You may also want to restrict simple starches and sugars in your diet. Doing the above may help you avoid thrush (a yeast infection of the breast) that could make your complicated situation even more complicated.
Hang in the, mama!
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"