How Long Does Housetraining Take?
It's important to remember that your Lab is still a baby in many ways. Just as it takes months to toilet-train a toddler, it also takes months to reliably housetrain a dog. Be patient during this process. Yelling at your dog when you find an accident only teaches him to sneak around and find secret places to potty. He may even avoid peeing or pooping in front of you at all, which really slows down the process.
Remember, too, that until he's at least six months old, your Lab isn't physiologically capable of controlling his bladder or sphincter for long periods. The muscle control just isn't there yet, and it's not something that can be hurried along. That's why you need a crate and a schedule.
Never assume that your Lab is fully housetrained until he's been reliable in the house for months without an accident. He may have occasional setbacks until he's a year old. If that occurs, make sure you still have him on a regular schedule. See if there are changes you can make to give him more opportunities to go outside when he needs to.