The reason you can remember less and less from your past.
The reason you can remember less and less from your past can be summed up as follows:
Think of it in terms of layers of opaque glass. If you have a picture and lay a piece of opaque glass over it the picture is still there but fuzzy and diminished. When you put another piece over top of that the image is more obscured. Put another piece on top and you can barely see the image. After a few more pieces the image is nearly or completely gone.
This is what is happening to you. Since we are all at a point of inviting new layers of our higher self into our physical bodies we are also bringing in those other lifetimes and experiences. It all begins to meld together for your greater good but some of the details of the past need to fade.
This is why more and more you are losing the details of old memories. It is a good thing since you are bringing in more and more of your true self. Rest assured that if you need those memories they will instantly be back, but for now they have faded to allow you to focus on integrating the new layers of yourself that are coming in.