My 21 Year Old Son Is Having Sharp Pain In

My 21 year old son is having sharp pain in right side below rib cage, including pain there when deep breathing. Feels as if he is overexerted himself - went to ER for anxiety attack on 3/15- did chest xray and EKG at time- all good. Went to walk in clinic yesterday and was told he possibly pulled muscle from vomiting over weekend (little too much celebrating his 21st birthday) - fatigue, night sweats, distended tummy and bloated. Had showed a 4 pound weight gain within week - and he's not doing anything out of the ordinary.