Its not unusual to feel this way, especially if you are having a tough pregnancy or are having lots of medical appointments. Please don't be hard on yourself, its more common that you think.
I felt very detached and unable to get excited during my second pregnancy but had no problems bonding with DS2 and he and I have always shared a special bond.
If you have had depression before though and think you are starting to get similar signs/symptoms, one important thing to consider is the possibility of Ante Natal Depression. Its not as well known as PND but surprisingly common, although many women find it hard to talk about, even with their midwife or doctor.
If you think this might be a possiblity, please try talking to your midwife about it and see what she thinks. You can have treatment and counselling for AND and it is usually very successful. Also it doesn't necessarily mean you will go on to get PND especially if the AND is caught and treated early on.
I am sure this is not the case with you though, just somthing to bear in mind. Its hard to be excited about being pregnant when you are feeling tired and having lots of medical appointments etc. Try to be kind to yourself, you are not alone, lots of women feel this way during pregnancy.