Hi there ,
Sometimes after shaving its quite normal to have an itch as the hair grow out of the sensitised skin.
So better to moisturise the area after shaving.
Now if all other things have been ruled out then there are two possibilities,either you have git some sort of infestation like Scabies
or Pubic lice
or there is contact eczema
of some type.
I would suggest to visit a dermatologist
because the treatment is quite different for these two conditions and without examine it physically and obtaining more history from you I can't comment any further.
I hope you understand my point.
Thanks very much and all the best.