An exclusively BF baby should not have that much difficulty trying to poop. The way you are describing it, it sounds like constipation. You might want to examine your diet in case he has a sensitivity to something you are eating (dairy? wheat?) Do you think it might be gas, or reflux? I'm assuming based on your lo's age you haven't introduced any cereal/solids yet that would be interfering.
I am not a routine expert, but if you post your routine, someone might be able to offer some suggestions as that could be contributing to night wakings as well.