Hello there we understand your feeling and your pain and hope the pain of yours is not bothering you too much. It is common with very one who runs a marathon there would a bit of pain atleast. To be precise your pain is more intense let's assume like that. Before straying any marathon 1 st and basic need is to stretch your muscles legs atleast for 20 mins. You.May have practiced running many time Times but they are incompletely strong when they ate nit subjected for stretching. so try running after stretching and also do it after running too. You'll see improvement by yourself. if that is mot working then consult a physiotherapist. Thank you