Is it normal that i can't cum?

Hi I'm 22 years old and I still can't cum I started having sex at the age of 18 and I didn't noticed It until my boyfriend now is so eager to make me cum , we tried everything his very good but I could feel it coming but it won't come out and I had this terrible pain if I can't make it out. My boyfriend is very good in sex . I just don't know why I can't make it , it would be 3:0 is the ratio of our cum 3 for him and 0 for me. I can't fake the cum coz my boyfriend would know it. I just want to cum to him so he'll be satisfied . Any help?