hi just wondered if anyone knows how soon i could go on maternity leave after just returning back to work (planning number 2) i work for the nhs.i have got it in my head that its 3 months

I believe that being on maternity leave counts as being employed by that person so it classed as continous empolyment.
so you would be entitled to maternity leave whenever you decided to get pregnant so long as you stayed through your qualifying weeks and until you were able to finish again.
If you get extra benefits from the NHS like extended maternity leave or a higher rate of maternity pay than SMP then there may be extra requirements for you to be there a certain ammount of time to be able to attain them. do you have a head office or HR department that would be able to tell you?
good luck with no 2!