My son who is 16 just had his 3rd Entyvio infusion. After the first infusion his only complaint was moderate back pain like between his shoulder blades. After the second infusion it was back pain in the same spot and a bad headache like a migraine. Now it is 4 days after his 3rd infusion and it is back pain and headache and stomach pain(but I think that could be because he is only on 25mg of Prednisone right now and the Entyvio just now has got enough in his system to start working). I was wondering if anyone else has had these same side effects and should I be really concerned?