Problems with Mastectomy Scar

Hi Ladies
Me again!! Should have known I would have more problems since every phase of this treatment so far has raised issue after issue.

Anyway had a mastectomy on 17th of Sept so 4 weeks tomorrow. Suffering with chafting and rash/redness all around scar underneath both arm pits (had auxilary clearance to right). Had a big chest so mastectomy bra with softie prosthesis leaves me very unbalanced and I think mastectomy bras come up higher under arm so digging in.

So rash, redness and soreness all over that area. Has anyone had this? Any advice would be greatfully received. At my wits end ...in attempt to keep remaining boob at the same level as whoopie cushion I am cut to bits and have all this rash and redness. Cue selection of expletives.....

Thanks ladies.