This morning my son woke up with a rash on his body. The rash is red, mainly on his stomach and back area and upper inner legs. Nothing on his face. It looks like big birth marks.
What can it be?

It could be bed bugs, if I dosen't go away soon take him to a doctor. If it is bed bugs and it gets bad you could end up spending a lot of money to get them all out of your house so try to figure it out before it gets to bad

Has he had all his shots yet? If not I would take him to the dr. if he has a fever I would not wait

Has he been exposed to chicken pox?

Don't take the advice of strangers over the internet as a concrete diagnosis. Your child NEEDS to be checked out by your pediatrician for a proper diagnosis and treatment.