For 1, I don't think that they will care. Lots of people switch careers and go into medicine (even though that's not your intention). If it really bothers you, perhaps you could get some clinical/medical related volunteer service done during your MS pursuit to show that that you do have a genuine interest in medicine but that you also had unfinished business in CS to complete.
For 2, people have matriculated with many Ws. You would of course explain your reasons for receiving Ws in you personal statement. As far as not having social science/humanities, med schools like to see well-rounded students and they almost always say that having that sort of educational background is recommended but not required. Maybe you could take some online, or in person, courses such as ethics, nutrition, and psychology courses at a community college.