What can I do about my seroma?

Hmmm- why won't they consider aspiration if you are uncomfortable? It's safe and easy, and that procedure is really not taxing on a system like the NHS system... (it's quick and doesn't require costly instruments or highly trained staff...) 

In the meantime, some compression on the area (not too much, you shouldn't be in pain) may help somewhat. Ensuring you have good nutrition to allow your inner surfaces to heal is always a good idea (low sugar, high protein, vitamin C), and avoiding too much salt or water is not a bad idea either? 

Seromas are not uncommon after surgery as it is natural for the body to secrete fluid after trauma (and what surgery is not traumatic!). They will absorb on their own, eventually. I am not sure why your physician will not consider aspirating the fluid but maybe they feel it is so tiny that aspiration will not affect your comfort/ or poses some risk.(underlying implant?) If your physician is not comfortable aspirating the seroma, it can be removed under ultrasound guidance by radiology. Compression with a tight bra or ace wrap may facilitate resorption as well as avoiding flying (in an airplane), consuming less caffeine and salty foods. Good luck and take care.