Whelp means "a puppy/pussy".
You know the saying, "If you can't run with the dogs, go sit on the porch with the rest of the puppies." It's kind of like calling someone a pussy. EX: Dude, you're a fucking whelp puppy, pussy
. EX 2: Someone goes to a concert on a Sunday night and has work the next day, a REAL man would go, but a whelp a.k.a. pussy/puppy
would stay home because he wouldn't "feel up to it".