Frustrated with EBF .. Help please

Nicole
I am getting frustrated but things have been going well I am just going through a rough patch and don't want to give in. My son is almost 5 weeks I plan on EBFing him until at least 6 months. My frustration right now comes from not knowing when he is full and his constant latch/unlatching after initially staying latched for only 5 mins or so. Sometimes he will even pull with my nipple still in his mouth. 
At times I think I keep trying to feed him when he might already be full but other times I feed him and think he's done and 20 mins later he wants to eat again. 
Any advice is helpful and welcome!