Although med school is certainly not impossible, you have a lot of work ahead of you in order to make yourself a competitve candidate. I’ve responded specifically to your questions below, but just wanted to make a couple of general comments/questions. First, was there any kind of upward trend with your grades? That is, towards the end of your degree, were you getting better grades/were most of your poor grades at the beginning of your college career? Or, were your grades mixed throughout?
Second, I don’t know all of the circumstances, but I notice that you managed to graduate from college (albiet in a rather long time) after having a child at the age of 16. This can be turned into a positive, although you need to be thinking about how you can explain your lengthy first degree to adcoms. You don’t need to explain it to us, but you will need to be prepared to explain your record on applications.
1) Should I take non matriculated classes on my own or should I enrolled in a Post Bac program? Advantages and Disadvantages of both? How would Med Schools look at each?
Given your history, I'm going to say that it might be to your advantage to enroll in either a formal postbacc program or consider doing a second undergraduate degree. You need to show that you can do well in a full load of courses and complete requirements in an expected period of time.
2) Given that I take all pre req (even the ones I took already) for Med school and do very well in my classes, how would Med Schools look at my undergrad GPA?
No doubt, it's going to hurt you. It's going to be very difficult to bring your GPA up significantly, especially if you have already taken most of the pre-reqs. You need to show that you are capable of handling rigorous coursework. If you can show a trend of excellent grades in upper level science classes and do well on the MCAT, it will help you considerably.
3) How would the fact that I am taking some classes over and I have a low undergrad GPA influence the decision of Med Schools accepting me?
This really isn't significantly different than question number two. Any pre-req course that you did poorly in and/or feel you didn't retain the knowledge from very well, you should probably take over. Additionally, you need to take some upper level science courses that you haven't taken previously.
If you are interested in DO schools, I believe your lower grades can be replaced by new grades, improving your GPA on a DO application. It will still show that you retook the courses, but will allow you to have an overall higher GPA in your application. Hopefully, one of our DO students/grads can clarify this process for you a little bit or correct me if I'm mistaken on that point.
Again, I think you should seriously consider either doing a new degree or a formal post-bacc. There are different types of post-baccs. Many of them have extremely competitive entrance requirements.
As Bill mentioned, don't forget about volunteering and clinical experience and the importance of doing well on the MCAT.