I need you help please :(?

my son is nearly 7 months old and every day without fail he will cry for over 1 hour sometimes 2 hours i pick him up, change him,feed him, give him cuddles, sit him on my lap, give him teething gel and calpol but he still cries its always around 5:30pm when he does it i don't no what else to do for him i have mentioned it to the doctors quite a few times but he just says there is nothing wrong he checks for colic and infections but says there is nothing wrong and every things is ok he gets to the point wear he struggles to cry what could be wrong? most of the time i do believe its because he is over tired because he wont sleep throughout the day but at the same time sounds like something is hurting him any ideas?