I agree with KTowne, keep them updated but don't push the issue. Either way at the end, someone will have to step up. Hell, I know who my baby's father is and because he is no longer interested since we spilt up, I just occasionally text or call when I go to the doctor to keep him updated on the progress. I don't expect anything from him, that way I'm not disappointed. I'm not saying it's easy doing it all on your own, but its damn worth it. I have been single since I was about 10weeks along and I am now 30weeks. Just hang in there and don't stress or press the issue. It will fall into place sooner than later. You can totally do this on your own. Us ladies are here ( I know that may not seem like much but it has helped me a lot with questions, concerns, advise, seeing all the diversity, or just getting a good laugh and most of all support). You re not the only one going through something like this, and you definitely wouldn't be the only single mom.
i would just let it be, update them both (via text, call, person, whatever you normally do) about your appts, because in the end you need to treat them both like they're the fathers in case they turn out to be the father, if they don't respond or step up, leave it alone, you can't force someone to want to step up or support you and their (possible) child, and the only person that's going to suffer is you and your baby, do you have family and friends to turn to? i know it's not like having a babies father, or friends and family, but you always have us on here to support you.. this is going to be a hard time for you but in the end you are going to be one STRONG mama, and you're going to find some serious inner strength the first time you hold your baby, trust me, there is no strength like a mama bear! :)