16 week old baby not cooing suddenly.

My 16 week old baby boy was cooing a lot before. Since 5-6 days he has stopped cooing. He just smiles when we talk to him and sometimes makes mild noises with his mouth closed. I was on antidepressants during pregnancy and now aswell. He is exclusively breastfed. I don't feed him directly for 4 hours after taking my meds. I pump out most of the milk after 4 hours and discard it. In that 4 hours, I give him my previously expressed milk. Can this be because of me taking antidepressants? His weight gain and urine count is normal. His head circumference and height are normal. He was tested for developmental milestones 3 weeks ago and it was normal. The past 2 weeks have been stressful for me and my family because my father had a tumour removed from his head so we couldn't concentrate on my baby much (didn't converse much with him since my mom and I were busy with my dad's operation and stuff). Could this be a reason for him not cooing..? Is this normal? Should I do something about it? Help