Instead of making seams, select a row of faces that separates the mesh along the front/back dividing line. Switch to UV Face Select. In front view, Unwrap>>project from view.
You should get a row of faces defining the outline of your mesh, and it should be symettrical. You may need to tweak this so there are no overlapping faces in the UV Editor window. Pin all vertices.
Return to Edit mode, and select all the faces in the front of the mesh. Switch back to UV Face Select. This time, just unwrap. The front half of your mesh should now be symettrically unwrapped. You may have a few overlapping faces to fix, but there’s probably a whole lot less of that than what you were faced with before.
Return to Edit Mode, do W>>Select Swap to get the back half of the mesh selected. Switch back to UV Face Select and unwrap the back half.
This method will work for parts of the mesh that are facing front or back, but not on parts that are at angles, such as the hands and feet. These you’ll probably have to unwrap separately.