Is a very bloated stomach a sign of stomach cancer?

I work out regularly including cardio and weights but my stomach seems to be getting bigger.
My doctor said it's just my body shape but it never used to be this way. It's getting so blatantly obvious something is wrong. I have fit legs and arms and back but this huge stomach.
I was wondering if it could be a tumour, since they are extremely difficult to find. Should I call a oncologist or some other specialist for tests?
Added (1). @April The problem is if my doctor doesn't believe there's a problem then how can I get a referral to an oncologist?! I have to get in somehow?
Added (2). Thank you all for your answers so far. It seems I won't be able to get a referral if my doctor doesn't think there's a problem. So, I have to find another GP to order tests?
I have read that stomach cancer is one of the most difficult cancers to find. I knew a man who had stomach cancer and by the time they found it, it was stage 4. He died within the year.
Rob Ford, the former mayor of Toronto had a tumour which wasn't detected until he went to the hospital with unbearable stomach pain.

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