The original poster had been using a Feather DE, before trying a straight razor. IMHO, a Feather DE blade is a good proxy for a really sharp straight razor, held at a proper angle against the skin.
Two questions:
1) Were you doing an ATG pass with the Feather DE?
2) Did you have razor burn with the Feather DE ?
If answer to (1) is "yes", and answer to (2) is "no", then either:
. . . your straight-razor edge is not as sharp as the Feather DE, or
. . . you're using more pressure on the straight razor, than you used on the Feather DE, or
. . . you're using too steep an angle for the ATG pass (which is easy to do!).
If answer to (1) is "no":
. . . See what an ATG pass with the Feather DE feels like (very very light pressure -- the ATG hairs tend to pull the edge into your skin!).
If no razor burn that way, your straight razor needs honing or more stopping, or you should reduce the pressure you're using.
. . Charles