I experienced the same pain around that time. It was so unbearable I had to call my Dr because I was scared .. she said it was my pelvis stretching to prepare for labor and said theres nothing I could do :( i used a heating pad and dude it worked wonders!!!! I am now 27 weeks and had the pain again yesterday i didnt waste no time this time to use the heating pad! And i woke up today perfectly fine :) at least so far lolĀ
Perhaps he is sitting in your lower back... so he's posterior and you can't feel his kicks as much, not 100% but thats my guess. :)