Kelly, 19, from Norwich, was one of the hit acts on the Simon Cowell talent show last weekend, after his acoustic performance of 'Make You Feel My Love' silenced the crowd and judges.
Speaking about the response, Kelly said: "It's incredible. I've had under 100 followers for a year on Twitter, so to get to 6,000 in days is incredible.
"After scrounging around for money and trying to get as many gigs as possible to keep myself in pocket, it's amazing to now have all these people talking to me and wanting to hear more from me.
"I do four or five gigs a week and I've been doing open mics all the time. I was doing original stuff, folksy blues bits with a band of guys. We've been doing gigs and making just £10 or £20 for a gig for quite some time.
"I've done some festival and support slots with another band as well, but nothing major. I've always just been trying to get as much experience under my belt as possible."
Kelly, who now lives in Brighton, said that he had "no idea" that the BGT prize money had been boosted to £500,000 by Cowell this year, claiming that the old £100,000 fund was already "mind-boggling".
"I've always been £1,000 in my overdraft so I wouldn't know what to do with that money. I think I'd have to give some to charity," he said.
Britain's Got Talent continues on Saturdays at 8pm on ITV1.
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> 'Britain's Got Talent' live blog
Watch Sam Kelly's Britain's Got Talent audition: