I sympathise! My DS (2.7) has never shown seperation anxiety and frequently asks for Daddy/Granny/Grandpa over me.
Also if I do go away he hates it when I come back and often if his Granny comes to watch him he says 'bye, bye Mummy!' as if he can't wait to get rid of me! Even when he is ill/fallen he asks for Daddy, not all, but a lot of the time.
I had PND/anxiety and a terrible birth and although I bonded with him fine despite this, I sometimes worry about how well he has bonded with me. Even my Dh makes comments like 'oh he really responds well to you now' as if there was a time when he didn't.
BUT, I am with him most of the time as I only work one day a week. He has never been to nursery and if I ever leave him it is with Daddy or close family. I have come to realise that I am the constant/given and he plays up most for me because he knows he can, I am his Mum! We do fun stuff together, swim,bake,paint etc but I will never have the novelty factor. He has a very special bond with his Granny, who has been a wonderful help to me. This is a positive thing and he is just a very secure child. Why should he cry for me when if I leave him it is to be spoiled by Grandparents? My DH is a natural and wonderful father, who also struggled as a new Dad but has developed a very special bond with his son. Whilst I sometimes feel a little jealous, would I have it any other way?
Your concerns are normal. Mums have a need to be loved too. I have had some bad moments/days where I was sure my DS didn't love me. It doesn't help that my SIL's DS clings to her constantly! But then she is jealous that my DS plays independently and that I can go out and have time to myself. But I am so sure that your DS loves you to bits, he just doesn't need to display it openly because his secure attachment to you just is. You said you love him to bits, that is all that matters.
I am pregnant again and feel awful with tiredness and nausea. I am so grateful at the weekends that he wants to be with Daddy, I get to rest a little!
Sorry for the waffle but hope it helps. Your post struck a chord with me