Had ectopic pregnancy at 4 weeks and removed on 30 dec.Left tube was not removed only damaged.doctor said we could try to trying to conceive immediately.not sure but on the 1 Jan I saw a clear sticky strecthy discharge.Could I havle already been ovulating.well we started trying to conceive on the 1 Jan.could I get pregnant already without having my periods.today I am feeling a bit nausea.could this be from the operation

It's possible you ovulated, depends on where you were in your cycle. It may also have been a response from the recent surgery. Yes, you can become pregnant before you have the next period as you ovulate before a period. It is not likely, but certainly possible.
It isn't likely that the nausea would be from a pregnancy that soon as if you did happen to conceive from sex on the 1st, implantation would still be underway.