vomiting, rash, distended stomach

My son is 15 months old, and about a week ago I noticed that his stomach was distended. Three days ago he vomited 3 times, and now I have noticed a rash on his back, arms, and legs. He has an ASD, and he was born with pulmonary hypertension. He also woke up one night, and his lips appreared swelled, and his cheeks were red. All together these symptoms concern me. His pediatrician said that he has a virus. There has been no fever or other GI symptoms to reflect a GI virus. She felt his stomach, and he did not have an enlarged liver or spleen, and she said that the distended stomach appeared to be air and not fluid. Should I request blood tests to make sure his white count is normal? What other tests would you recommend.

my son also has a distended stomach and i found an article that may fit some of your sons symptoms healthatoz.com/healthatoz/Atoz/common/standard/transform.jsp?requestURI=/healthatoz/Atoz/ency/celiac_disease.jsp
is the page on celiac disease, it talks about ditention and vomiting onset posibly by a virus and also accompanied by a rash.