I can not play because of lag or whatever

I dont understand, I am playing online and when ı started to match ı can play only first half after that ı cant play because of lag and thats not minimal that become unplayable but first half everthing ok about game. This problem also continue when ı open a pack. everything ok in menu but when ı open something it start again, in cutscene players come laggy after that menu become laggy matches are laggy, unplayable thats not fun ı cant fix it every match same thing what should I do