Yyears ago a soup can fell on my foot leaving a large lump. over time this lump has always been there but some days it's smaller others it's rather la?

Can Can: Without examining, it is difficult to say, but the story probably goes something like this. The can caused soft tissue damage which led to the initial lump. The soft tissue damage may have initiated the formation of a ganglion cyst. The extent of the damage might have also damaged the periosteum of the underlying bone causing further bony damage. To remove all doubt, have your foot examined.