I can only wear cotton shirts etc and any hint of man made fibres seems to exacerbate the "armpit" whiff.
I noticed it recently when I bought a padded shirt from amazon and it tends to make me aware of a smell.
Obviously, hygiene with hot water and soap normally works, there is a medical soap/cleanser thetas more antibacterial than other household soaps, plus a clean shirt every day.
on the odd occasion that I became aware of a smell I got a bottle of surgical spirits and used a soaked tissue to wipe my pits with alcohol. - even meths! Your age might make it hard to buy?
what about getting some surgical wipe sachets?
Like the kind of wipes KFC used to hand out but with an alcohol element
Take the above advice with caution as I have no medical training