Not eating

[chris-uk]

Its been eating mostly fish.

You're going to need to give us a bit more to go on if you want any useful help or advice.
We don't know how it's being kept - viv size, heating setup, lighting etc.
We know it's not eaten for three weeks, and before that it ate fish. What sort of fish, how often, any change to feeding over winter?
Have you brumated it?
What species? Age?

[Invisible Snake]

About 60 you say? That would be why.

^^^ Exactly. OP's snake is most likely not eating because of the cold temps.