Need advice communicating with birth family

This is going to be long, so I apologize in advance. I was adopted in a closed adoption through the State of Minnesota and the children's welfare agencies of the respective counties of my adoptive parents and birth mother. I was about 6 months of age. My adoptive parents told me when I was very young and showed me the adoption papers and all the information they had about my birth mother as I grew older, which was very little and nothing identifying her. They had no information about my birth father. I sent a request for my original birth certificate to the State of Minnesota late last year and this past March (the day after my birthday of all times!) I was contacted by a woman from the county child welfare agency that assisted my adoptive parents through the adoption process. She had sought--and received--permission from my birth mother to give me her information. The next day I emailed my birth mother and we've been corresponding by email ever since. She asked specifically that I not call her yet. She's shy, as I am, and says she not ready to speak with me on the phone, even now 3 months later. My birth mother, her sister and her mother (my birth grandmother) all say the whole family is thrilled to have found me and are excited to get to know me better. I have no reason to doubt that, but I'm a little concerned there may be something they're trying to keep from me. No one seems to want to tell me the identity of my birth father, or even discuss him or that time in my mother's life at all. A few adoptive family members do not respond at all when I try to contact them by email or Facebook. I would be happy with just a "it was a difficult time in my life and I'm not ready to discuss your birth father or the circumstances of your birth yet". I've emailed (I wish I could call, but I understand and am trying to be patient) asking that my mother tell me his name. I tried to be very tactful and sensitive, trying to put myself in her shoes. I even promised I would not make contact with him if she would be uncomfortable with that, especially if he hurt her in any way. It feels like there's a secret they're trying to protect, but maybe I'm just letting my imagination run amok. The lack of knowing has led me to consider all sorts of reasons they might not want to tell me who he is, everything from she loved him and he abandoned her to she never told him she was pregnant to he raped her. I'm a pretty grounded gal, and I'm not assuming anything, but the secrecy I perceive (correctly or not, I don't know) is leading me to ponder those kind of scenarios. My adoptive family is very loving and good and I love them dearly. It was a very small family, though. I only grew up with my adoptive parents, one brother who was also adopted, my grandmother and an uncle who lived one state away. Even though I knew they loved me I never really felt like I belonged. Perhaps it was because I was extremely shy in a small family of very outgoing, gregarious people. I always felt a bit like a black sheep. I want so much to "belong" to my birth family, but I keep reminding myself that this will take time. I'm starting to worry, though, that I'll never belong with them either because, even though they say they're excited to get to know me, they seem to be holding me at bay. I guess growing up knowing I was adopted left me feeling unrooted, unanchored and feeling like I didn't "belong" anywhere. Finding my birth mother and her family has helped greatly in reducing that feeling. Knowing the identify of my birth father and his family would as well. I'd love any advice, especially from any birth parents out there who have given a baby up for adoption. Thanks so much.