The razor you're using may be too aggressive for your skin. Also use absolutely no pressure just the weight of the razor itself. Try holding the handle nearer the head on those areas where you are getting irritation. Start with the top of the head against your skin and slowly lower the blade edge until it stats cutting your beard this will give you the exact angle to use.
Don't continually go over the same spot make sure you religiously do WTG, XTG maybe East West and West East, ATG. Finally try missing the ATG pass on the areas causing you problems.
As others have said keep your lather well hydrated and rinse the blade often.