I am about the same level you are, my advice may not be great, but here goes.
After watching your replay, these were some flaws I found:
You built 2 evolution chambers and they sat dormant for a long while only to be used once, however this isn't a huge deal since you had so many minerals.
You had too many minerals. You were building all roach/hydra and gas was your limiting factor so you have to throw in a mineral drain as well or its just going to stack up. I would have probably built some zerglings throughout the game and maybe another hatchery in your main.
Scouting is important. You had a ton of overlords (and a lot of overseers for some reason) just sitting around doing nothing. Spread them around the map some. You had the xel-naga watch towers, so you could see the middle but that really doesn't mean much since he did drops. Also you sent your army on a suicidal attack, you might want to send in an overlord first so that doesn't happen.
He was a giant blue turtle, so gain map control. This goes with more scouting, but if you see him being highly defensive then expand some more. You could have taken the entire right side of the map without him even noticing. However when you do expand, make sure to use that base. Your third base did nothing for a long time, then it only mined minerals when you really needed gas.
You also might want to try harassing some. Get some mutas or zerglings to attack every time he thinks about leaving his base. This will make him become even more defensive which lets you really easily expand.
And try to produce more. I had the production tab open for the game and there were long periods where you were producing nothing. You had the supply, larva and resources, but I guess you were lacking motivation or something.
And don't be afraid to change your plans. You seem to have been set on going roach/hydra, but I bet if you would have thrown some banelings at his marines/marauders he would have been most upset.
Well, that is all I've got. As I said, I am not that much better than you (especially as zerg), so if something I said seems stupid, it probably is, so don't listen to it. Besides that, just watch your replays, watch day9 or other castors if that helps you and play more.