Any Pediatric doctors out there?

I have a 3 year old daughter who has had a hoarse cough with phlegm for about a month.. at first the doctors told me it was croup....when she didn't get better they told me it was a virus...when she developed a rash (which has gone away now) on her neck face and arms they told me it was viral rash and not to worry...and now she has a bulging vein on the right side of her neck...it is about 1/2 inch think and runs from the top of her neck to the bottom. I am taking her in again tomorrow, does anyone have any suggestions what it could be? Or what I could ask the doctor to check? I am extremely worried about her. Also, other then the cough and vein she seems healthy and energetic. One more important note, she has developed dark circles under her eyes, and she is not dehydrated or malnourished at all.