I wonder if perhaps as an adoptive mother you are putting even more pressure on yourself than a birth mum would?
My experience as an adoptive mum and supporting other adopters, is that this is very true. Adoptive parents do tend to put themselves under a lot more pressure.
For many this is the culmination of YEARS and years of yearning for a child, and dreaming of that day you will finally have your child. Of months and months, and maybe even years, of interviews, and paperwork, and questionning and preparation. It's incredibly emotional, a rollerocaster, and it's intense. But this is the moment - this is what you've been aiming for for all this time, this is IT, and oh boy do we have expectations, however uncoscious those expectations are. We want so desperately to feel love as soon as possible. We expect that because we've been trying SO hard and been through the tough (for very good reasons) adoption process, that our dreams coming true must mean our dream will be dreamlike - with love, and a desire to spend every moment with our child, and without us sobbing or feeling nothing. We don't want to, or can't, envisage having such a tough time post adoption, or envisage ourselves not quickly falling in love with the child we so desperately wanted to parent.
I didn't come to adoption through infertility, but after 2 years of adoption process, I also expected myself to love. I didn't expect bringing home a 10 year old to be dreamlike, but I expected myself to have these emotions that didn't come. I didn't expect to find myself resenting her presence at times.
It doesn't help at all that this 'love at first site' thing is such an ingrained idea, especially when it comes to adoption. Strangers, family, friends, all may have this lovely picture in their heads of the person/couple who was desperate to experience parenthood meeting the child who needed parent/s, and voila, they met and it was instant love, la di da. But adoptive parents can pick up on this expectation, however unsaid, which just makes it worse.
And there's another reason too, I certainly felt this. And that's that we expect ourselves to be perfect for our children's sake. From day 1 of the adoption process, the backgrounds of children in care are made clear to us. As is the fact that most children may sometimes (or all the time) need different parenting than a birth child. Basically, we quickly come to know how much our possible future children may have been through, will go through, and need from parents. Hence we place an expectation on ourselves of doing and being things that aren't humanly possible. I MUST love my new 10 year old daughter soon because she deserves it, needs it, how can I not when she's been through so much? I must be able to parent the way she needs, however stressful and difficult, straight away. Because it's not fair on her if I don't. I CAN'T resent her right this second, and want a break, because damn it, I'm the adult and she's the child whose been through so much and needs me to think the exact opposite of this. We can feel like we're failing our kid if we do the minutest thing wrong, beause we're so aware of what our kids might need every second, all the time. And it's definitely not the same as with a birth child, because we are trying to parent after knowing what our children have already been through, almost trying to make up for every bad thing that ever happened, by being perfect. All the weight of the preparation and impressions of what adopted children need from their parents is pressing down on you.
So many years down the line, I no longer think this way, but I went through these feelings and stress and sobbing to get here. I now know I can't expect to love, or be superhuman. And it's painful seeing new adoptive parents going through the same as I did often.
Sorry for essay in response to such a little question 
Be interested to see if the other adoptive parents agree with me