3 year old has strange rash??

My 3 year old has developed a strange rash.  i thought it might be fifth disease, but the pictures online don't look like what she has.  Her rash looks like someone whipped her with a belt.  They are long (3" or so) lines of raised welts.  They will be on her bottom one time and then and hour later be running up and down her arms or stomach.  they go away with benadryl but come back the next day.   She did have a little bug about 3 weeks ago which is what made me think it might be fifth disease, but like I said... the rash doesn't look the same.

Any ideas

[kitykan]

Sounds like Bartonella