Sudocreme sounds like a good option, but another one is pure aloe vera gel - you can buy it in tubes from Holland & Barrett (c. £6). Keep it away from your wounds though, and maybe just double check using it with your BCN.
I also had a little reaction to the dressings. A rash in a line where the adhesive was under the clear bit of the dressing. My BCN said she had never seen it before! I cut off the edges of the dressing where it was worse and put Sudocrem on it. I did worry that the dressings would fall off before I went back to the hospital though.
I am 8 weeks post op for a reduction on my left breast and within days of having my dressings changed I developed a rash on my chest. My breast is also slightly red and itchy. My friend who is a nurse had a look and said I should be checked out as it should not be red so many weeks after the op. After seeing my BCC nurse and GP I am told not to worry and now have eczema. I am sure it is a reaction to the glue used. I am putting hydrocortisone on the rash (now spread to my neck and back) and it is improving. I have not been told to put it on my breast. Perhaps I should.
I wonder if a different glue can be used for ladies with sensetive skin. Has anyone else had this problem I wonder.
I had a reduction in October - but on both sides.
I had areas of sensitivity at the nipples and where the scars are underneath, but not the all over soreness you have.
I was told to keep a bra on day & night for the first 6 weeks. I do think the support has helped with healing. The consultant made a fuss that I didn't have one on in the ward the morning after my op.
Have you tried the pull on bras? I have some Belvia bras. I didn't really find them supportive enough for daytimes, but I don't know how else you'd manage with a big difference in size. They have removable pads which I found useful to use as protection from the seams in sports bras. But they also helped my confidence starting back to work with smaller boobs. The cancer side is currently about 1 cup size smaller than the other.
It all takes time. My 'good' side is fine apart from some tenderness underneath when touched. It is about 10 weeks on from surgery now. I have had radiotherapy on my 'bad' side and that is v red and sore again and today I am wearing the belvia for cushioning under a sports bra. On week 2 of radiotherapy I managed an underwired bra for the office Christmas party. I'm hoping I will be able to tolerate if for New Years Eve too - but need to work on a plan B for clothes.
It might be worth having a word with your BCN to check that it is healing as expected. For rashes after radiotherapy they suggested hydrocortisone cream in my instructions - you could ask if the BCN thinks that would help stop the irritation.
I don't think I have been much help, but you have my sympathy and I hope it settles down soon.