I had a dr appointment and just kinda curious..

I am 18 weeks 3 days with my third baby. I had a dr appointment today and i mentioned i was pretty positive i have started having Braxton hicks contractions. I have never had them this early but i chalked it up to its my third baby and my body just knows whats up lol. Well he turned around in his spinny chair and gave me the weirdest look and said he didnt think im having Braxton hicks but just uterus pain from stretching. I know what braxton hicks feel like. My belly get tight and i have slight pain and then it slowly goes away. Its not consistent and its doesnt ever get any better or any worse and they go away when i lay down and drink lots of water. Now i LOVE my doctor. Hes absolutely wonderful but i just cant get myself to believe this is growing pains lol. He quickly asked if my other two were carried to term and i said yes one 39 weeks and one 36 weeks. Im just not sure why he thinks theres nooo way im having Braxton hicks. Anyone else have them this early?? Maybe i am wrong??