Hello there..... well its not unusual to feel that pain during pushup as you said.... usually sometime the angle of the toes and the speed with which we do push up can alter the body mechanics...already in pushup position the abdominal and muscles of the thigh are in stretched position.... any small mistake or loss of rhythm may cause the quadracep muscle origin to face trauma or the lateral muscle of the abdoman can also be unduely stressed. But dont worry...this is purely a muscular condition...(if diagnosed otherwise through evaluation) ...qhat you need to do is apply ice or the affected area if its recent incident...or else do hot water formentation if 3 or more days have passed... also spasm cannot be ruled out... do apply a gel based in diclofinac and muscle relaxant like cyclobenzaprine 3ice a day...your condition should be ok in 5 days. Stop gym for the timebeing and dont stretch your muscles till pain is more. Do resort back to me regarding any furthur querry.

It is probable that you have strained your muscle or injured your back. But for site of pain bit usual for both . I would advise you get a check up from a physio . Till then rest and taking break from gym should help.