how could i prevent shaving spots on my vagina?!

Don't ask how I know, but strippers have a trick for this. Apply underarm deodorant (preferably unscented stick deodorant with antiperspirant) right after you shave (I use Arid Extra dry) Also soaking the area with a warm bath first can help soften the hair which prevents razor burn. And use a good amount of shaving cream and a sharp razor :)

There are gels you can buy at the drugstore that you apply after you shave that area to not get bumps and razor burn- I know of one called No Bump. It stings for a couple of seconds but gets the job done. There are a ton of more brands, many to choose from.
You can also gently exfoliate before shaving with a sugar scrub. You can make a simple one from home- olive oil and raw cane sugar, and you can use all over your body or buy one at a store.
Or after shaving you can apply witch hazel, as it acts as a gentle after shave- this works on legs and arms too. You can find witch hazel in most drugstores or a health food store. Good luck!

See your doctor ASAP!