Starting Solids

Was wondering if those of you who have breastfed had any trouble introducing solids to baby? My sweet boy is 6.5 months and it seems like no matter what I try to give him it completely upsets his stomach and he's miserable. I know the AAP says breastfeeding only is fine for 6 months but our previous pediatrician wanted me to try and start him on solids at 4 months... That obviously didn't go well cause he was absolutely not ready but even now when I try I get the same response. Thanks!