Dibly I think we are a few weeks ahead of you in terms of length of placement, also with a young baby.
We have this thing where DD just looks away. If sat directly opposite me, she'll look to the left. Then maybe turn to the right, in a quick move, without any glimpse of eye contact. Nothing can get her to look at me.
It was worse in the early (earlier) days, and nowadays it still happens but is interspersed with periods of good eye contact and cheerful interaction.
I feel your pain - it feels soooo rejecting. In fact it probably IS rejection. And it is normal human nature that if someone consistently rejects you, you withdraw. Disengage. You don't bother anymore. Purely to protect yourself. It is not really possible to not feel it to be 'personal'.
I felt that urge so strongly at times. It is incredibly hard, to keep engaging, keep seeking that emotional closeness, keep trying, when all you ever get back is a studious gaze to somewhere else.
So here are a few reflections that help me get through this and keep on keeping on, maybe they'll help you too:
The first is, I think that sometimes when babies feel overstimulated or overcrowded or anxious or something, they protect themselves by temporarily disengaging from everything. And maybe if they are experiencing huge emotions, that they can't make sense of, but that have something to do with you; then in that moment you, despite wanting to be a source of comfort for the baby, are the one person that baby needs 'space' from most. So I tell myself that sometimes at least the rejecting behaviour may be down to DD simply telling me that she needs to take it slowly, needs more time and space, that I have been expecting too much too soon.
The second is, I think that being not-well-attached is only to be expected in the early days, and if baby were to present as perfectly well attached after just a few weeks, I'd be worried about indiscriminate affection or similar stuff. I think it does depend a bit on the age/stage of your little one - somehow I'd expect a very young baby to 'attach' sooner than an older child. Probably because the very young are so entirely dependent, and hence you get lots and lots of opportunities for meeting their needs. So I think you are right to 'listen' to your instincts - you feel something is wrong, there is still much work to be done in terms of attachment - but equally I feel that at just a few weeks into placement, it would be wrong to conclude that something is generally wrong with attachment. It might very well be that your little one just needs a bit more time to grow attached. So by all means do seek out ways to promote attachment, do theraplay activities etc., and do get help for yourself in dealing with it all, but don't despair - chances are that time will help.
And finally, the third is, I try to absolve myself from the guilt of not being perfect. I feel that DD deserves her 'third mum' to be on top of her game, and deserves not to be let down, so I start feeling very guilty when I don't respond to her immediately or cause her some distress or simply don't spend as much time actively engaging with her as I'd like. So I need to periodically remind myself that she will be all right, even if I don't do the right thing 100% of the time. It may be better for her if I always responded immediately, but it will be good enough, she will be all right, if I respond immediately whenever possible. In fact, it just has got to be good enough, because I cannot do more than do my best. And doing my best includes looking after myself as well, btw, in order to make this work in the long run.
Oh and a fourth (sorry) - I tell myself I accept her 'no' but don't take it as final answer. Ok so she is not right now willing to engage with me, I can accept that, but I will keep on trying/offering; and eventually she WILL.
You know, I always 'knew' that adopting wouldn't be an easy ride, that it would be hard. What I didn't realise is the subtlety of how it is hard. How can you explain to someone 'It is so hard, she never looks at me.' The words just don't capture the feeling, the deep twist of being rejected, again and again; it hits you on a primal, physiological level almost, it is hard to override your animal instincts and keep on engaging, opening up emotionally, seeking closeness and so on. It's draining and I think it helps if you acknowledge that e.g. don't expect yourself to be doing lots of other stuff at the same time. Household chores can wait, while you re-charge your batteries when your baby naps, so that you can then go back to keeping on keeping on when baby wakes up.
Good luck, I hope it starts improving soon!