Does he call 3 streets postflop when you bet? Or does he just call one or two streets, then you give up and showdown and lose a hand?
I'd suggest jumping off Lock and onto one of the more reliable poker rooms that Cardschat offers here as well (they offer plenty, like America's Room or Black Chip on the Winning Network, Bovada
, and I believe Carbon Poker
on the Merge Network. Any of those are better choices than Lock, more players and a more trustworthy business to work with).
If you end up playing anywhere except Lock, I'd be happy to look at a 5-10 minute silent video of your play and record my thoughts and post it on this forum (probably in the thread in my sig). Just shoot me a PM if you're interested in that, happy to help. That way we can look a bit more specifically about ways you might be able to improve (very hard to give deep and specific advice without seeing hands).