I used a homemade shaving cream on my vaginal area and had an allergic reaction to it.that area is extremely sore and very painful to urinate?

Slow to recover: Ouch. Inflammation from an allergic reaction can take a number of days to subside. Oral Benadryl and topical hydrocortisone may be somewhat helpful but it may be more useful to simply soak the area (in a tub or use a sitz bath) and then void into the water, and then ice/cold packs to the area. You may need to see your doctor if symptoms remain severe and persistent.