I think that your problem is Snorlax. It is blocking your way. Well, go to Radio Tower (Lavender town) and talk to the manager.He will give you EXPN card.Then go next to Snorlax (Vermillion city) and tune your radio to PokeFlute music.It will awake, so battle it and keep walking to find Pewter city. Hope i helped
he'll only give you the radio card if you first go to the power plant (north through the rock tunnel then surf) and then go to Cerulean (West instead of surfing after the rock tunnel) and recover the machine part from in the water in the gym (use itemfinder) then return it to the power plant and go back to the radio tower. After snorlax go through the Diglett Cave and what he said ^