Pain on a treadmill

raeth

I have recently started running at the gym and I have to say I really enjoy it.
However i have noticed that when I really push myself I get a stabbing pain in my back.
The pain Is on my left side right under my shoulder blade it is an intense pain similar to stitch.
Does anyone else ever get this? Is it just a stitch?

I am massively overweight (just under 290) and was worried it could be my heart but I think it is a little to low for that

Any ideas?

Cheers
Dan