I cannot cum!

Me and my boyfriend have been together for 5 years off and on. We took eachother virginity but we have had breaks in between since then. We also have a 1 year old daughter. We have sex almost every night. I had never came until right before i got pregnant. But since we have had out daughter i cannot cum unless i use a vibrator. Everytime my bf brings up having sex it stresses me out bc i want to cum but he gets kinda upset if i use the vibrator because he thinks that he cant get the job done himself. It takes probably 20 minutes for me to cum with just the vibrator. But only like 3 minutes if we are having sex at the same time. I try and tell him that it is not him and that it is me. But it still makes him feel bad. I am so comfortable with him and i dont know if it is from having a baby or what. But i just cannot cum with just penetration. Any tips or ideas of how to cut out the vibrator to please both me and mh bf.