I installed a 24 ft round pool. But I couldn't afford the electrician to come out and wire the yard... sooo I ran a 12 gauge 100ft extension cord to the pump. It runs but only for a short time... is there a fix for this other than spending a fortune on wiring everything>

What is the Code for this situation in your Town/City/Village? It would be irresponsible to give you advice which is dangerous.