50ish pound loss in 5 months

I don't have an exact number because my original scale broke, and my new replacement was weighing 5-8 pounds heavier. I've lost 50ish pounds in the 5 months since my son was born. I have about 15 more pounds to lose, and I'd like to build some muscle/definition, but with a new baby, my loss has been limited to diet alone for the time being. I've had 4 babies in exactly 5 years.

This first picture is at one in the morning the day I had my son, at about 191-194 ish pounds:
<a href="http://s138.photobucket.com/albums/q247/lisasommers/?action=view&current=484487_4149461090019_1741794054_n.jpg&quot; target="_blank"><img src="http://i138.photobucket.com/albums/q247/lisasommers/484487_4149461090019_1741794054_n.jpg&quot; border="0" alt="Photobucket"></a>

This is yesterday at 145 pound:
<a href="http://s138.photobucket.com/albums/q247/lisasommers/?action=view&current=426984_4149465850138_838381182_n.jpg&quot; target="_blank"><img src="http://i138.photobucket.com/albums/q247/lisasommers/426984_4149465850138_838381182_n.jpg&quot; border="0" alt="Photobucket"></a>