My dog has been very weak for awhile, act depressed & lazy, doesn't eat sometimes, and his gums started going pale today, but he's been having these issues for a couple months other than the pale gums which happened today... what could be wrong with my dog?

It could be any number of things which we can't diagnose for you online. It's time to get the dog to a vet.

Could be a bad case of worms. Grey/white gums usually indicated dehydration or a parasite infestation. You need to get him to the vet.

Besides the above, pale gums can also be an indicator that the dog could be bleeding somewhere internally. Please go to the vet

Yes, I agree with the advice given for sure. Take him to the vet as soon as possible. It could be heart issues, internal bleeding, worms, kidney failure. He needs attention. If a dog shows symptoms of illness they are usually very sick. Dogs don't like to show weakness to their humans or other animals, so if they do, you can pretty much count on their need for medical attention.