I recently played Yellow again and the first pokemon I caught was Nidoran♂, then Nidoran♀ then Mankey then Pidgey.
Get rid of that Nidoran♀ and Pidgey. Train that Mankey to a beastly level to kick Brock's ass and have Pikachu as backup. Also go catch a Spearow since he's a pimp, and level that Nidoran♂ to Nidoking. Do this and all is forgiven.