I think that the fact that you have/are having these thoughts and feelings ongoing means that you need to talk to someone. It doesn't mean that you need to fit into a box with a lable weather it be pnd, depression, bi-polar or what ever, you are having doubts about yourself and your capabilities and if nothing else you need someone on your side and some reassurance.
Living with family so close has a lot of good points but it also does have its downsides and you are already building the fear of moving out to your own place, with 1 or 2 kiddies, into a huge mountain and if your doing that now it will seem like an unclimbable mound by the time you end up doing it.
You have not had the chance to prove to yourself how good a mum you can be as you have had the family close and (by the sounds of your post) you have not had the room to grow into being a mum who has had to depend on herself to get thru the day. Sometimes I think more people helping and stepping in (or knowing that they will be there at a certin time) makes us feel less efficient as a mum and a person which can then lead to us doubting our abilities.
Enjoy the people and help you have around you at the moment, find someone you can talk to about your feelings - your GP or ask for some help finding someone, trust yourself a bit more and believe in yourself.
Keep posting, keep talking, dont give up until you find someone who is ready to listen to what you have to say as it is important!!!