I feel really really depressed ?

I've felt the same way sometimes. A lot of these symptoms can be stress or anxiety related. I find a lot of times that when I'm really stressed out I experience chest pain and it feels like my heart is beating irregularly. If the doctor says that you're fine, you probably are, but if you really feel as though someting is wrong, then you should go see another doctor or a specialist to make sure. Otherwise, maybe talk to someone about your anxiety and try to see if there's a better way to handle it or prevent panic attacks. It'll definately help :)