1st child responding oddly to pregnancy

I'm 11 weeks at the moment and my first (m, 4.5) has started to become boobie/ boobies milk obsessed. He has not been breastfed in 2 years and as such we haven't talked about it since.

Just keeps coming up to me saying mummy can I have a drink? And when I say of course thinking he wants his usual drink of juice he points to my boob or puts his head there. He's done this a few times and I always explain he's a big boy and that boobie milk is for the baby. I do offer an alternative milk instead.

I wonder what's brought this on? Could it be hormones? My scent? Memories of being fed coming back? Children at school? Something someone else has told him?