Nodes swollen

I first found a lymph node swollen in my cheek at the age of 6.now im 18 and that node is no longer swollen hopefully.however,i start to get other nodes swollen at 15,and now they're still there.sometimes hurt and enlarged,sometimes just get smaller and without pain,but they never seem to disappear.i have consulted doctors for many times,i go and see different doctors.i even gone through the blood test in the local hospital,they tell me everything's normal and ask me not to worry.They tell me it maybe a cold infection,pimples on face,or anxiety that leads the problem.but i get nodes swollen in pelvis,under chin,neck,front and back of ear and lower cheek(near jaw),they're small and tender and i can feel them.there must be reasons for them to exist.i dont have big pimple problem,i have breakout during exam period,especially im having my A-Level exam in march and april soon,some people have more severe ance problem but they seem all fine,i just worried,wondering whats wrong with me?Thanks