Yes, it's quite common that people have multiple disorders and even more so when it comes to a lot of the personality disorders. You may have some of the more easily identifiable traits of PTSD, alongside depression.. and something that is important to remember is that it is a spectrum.... it is not black and white.
That's a tough question in any circumstance and hard to answer without fully knowing your situation. Either way, I strongly suggest that you try not to let ANY diagnosis define you. Do as much research on the topics as you can so that you can have your own informed opinion. Make sure to ask all of your mental health professionals as meany questions as you can, especially when it comes to medication. Also, I've found that the best consult for certain issues are the people that actually have the illness and/or are taking the same medication as you.