Help! Lump On The Guppy's Tail

[Auditor]

Hi, my guppy male has a lump on his tail.
It is big considering his size, 1-1.5mm and growing bigger. The lump looks as a congested blood vessel.
Treated him with salt and some antibacterial stuff - no changes.
He eats well, still chasing girls but getting tired quickly and rests on the bottom of the tank.
Please help!
Many thanks
Olga

 

[WILDER]

What colour is the lump.
So you mean a pool of blood in the lump.

 

[Ronananator]

weird same here is it on his anal fin