I'm a 29 yr old female with constant chest pain. i've had a complete heart check up. should i be confident that it is just stress or muscular?

Unlikely to be heart: because of your age any chest pain is very unlikely to be heart related. If you have had cardiac testing including an echocardiogram and perhaps a stress test, and this is all normal, it is quite reassuring that this pain is unlikely to be your heart.

Pretty much: If the cardiac workup has included blood tests, echocardiogram and stress test then it is very unlikely that the pain is due to your heart. Try seeing a chiropractor and beginning a sensible exercise / fitness program.