Self-hypnosis and past life recall

I've practiced self-hypnosis lately with great effect. Some of the things that surprised the crap out of me and convinced me it wasn't a camoflauged day dream were my ability to map out the floorplans of the houses I lived in when I was very young (three years old). Also I was surprised at how my mother looked (like a kid to me now) and my perspective at the time. I regressed myself further and was even surprised to find myself en utero. However, I can't recall any memories from before that time, and the three occasions that I have tried I just grow very sleepy and start slipping into dreams.

Is it possible that one can't recall previous lives, or that this is my first, or that this is an indicator of no previous lives?

Any tips on regressing past en utero?