The razor isn't always the cause of bumps.. While a dull blade can do that.. There are other ways to avoid it.
1.exfoliating the area to be shaved
2.using warm/hot water- try setting hot wash cloth on the area before shaving to open pores.
3. After shaving use cold water& or toner to close your pores.
4. Even better.. After shave gel or lotion that tones/balances PH to avoid irritation and ingrown hairs.
Also if you're really prone to burn try a shave cream/gel that is for sensitive skin