My doctor perscribed me prednisone for 5 days for severe allergies but I'm scared to take them?

Ok in moderation. Oral steroids can be very helpful in quickly relieving severe inflammatory diseases such as allergy. However, you should minimize the frequency by better controlling the allergies.
Short term use. A short term use like 5 days should not be something to worry about. Most side effects (that are scaring you) occur with high doses for long periods. Talk it over with your physician.
It's your choice. People are afraid of steroids because of the reported side effects, but miss the part about those side effects arising only after taking moderate to high doses of steroids for many months or years. There is really no downside to such a short course of steroids. If your reaction involves wheezing, you should take them; otherwise you don't need to take the steroids if you prefer to suffer instead.