Common, not normal
Babies will have many episodes of illness and rashes, so these are quite common but not normal by 6 wks.
If it is tiny/prickly little bumps (like-goose-bumps) and baby is acting normally, it is likely heat-rash. So, keep/dress baby comfortably and avoid excessive heat exposure. Check with doc for an eval to make sure..Congrats on new baby and good luck.