Hi, yes it can be GERD...more over it could be a hiatal hernia since lifting also exacerbates the issue for u.....
See a GI dr to start....look to family history for other issues that may be a factor for u, heart, etc....since u had testing on ur heart it appears fine, then u do not have to go that route again, GERD can cause it to feel like that , sometimes the vagus nerve is involved....
Do avoid foods that will trigger symptoms, greasy , spicy,acidic,alcoholic, carbonated bevs...keep a journal so u know...see a list in the Health Pages...
http://www.medhelp.org/health_pages/list?cid=236
Also modify ur lifestyle as well....elevate the head of ur bed, no tight clothes, no smoking, try to relax and avoid stress....