I think you have irritated the area by shaving it,sometimes it happens when the razor is not sharp enough or the hair are too thick and long.
Anyways not to worry, I would advise to start applying Fusiderm-H cream or ointment two times a day for 3-5 days and keep the area well miniatured by applying white petroleum jelly or Vaseline on between.
You can also take your anti allergic tablets as you have mentioned once day for 3-5 days.
I hope everything will be fine after the treatment.
Avoid harsh and perfumed soaps or products on the area and also do not apply any anti septic like Savlon
All the best.