What Causes Heart Palpitations, Tiredness And Clubbing Fingernails?

hi there, i am 24 years old/ 135lbs and am experiencing increased tiredness during easy tasks, constant palpitations (including pvcs and a general awareness of my heart beat) and what seems to be clubbing of my fingernails. my doctor did a ekg/bloodwork/o2 sats. ekg was normal, she said my ejection fraction was awesome, bloodwork was normal, and my o2 sats were 100%, she seems to think this all stems from anxiety and depression. i heard that 02 sats at 100% were not normal when not breathing straight oxygen. i know the likelyness of me having a serious heart/lung condition is low but its really starting to frighten me. ive had past ekgs which all came out normal, some even catching some pvcs which the doctor was not worried about. (ive seen 2 different doctors) should i look for a 3rd opinion?