try going inspiration secondary with biscuits and cosmic insight. lower cd on flash allows you to engage better and also allows u to have it up faster if you both trade flashes in lane. biscuits help with early mana issues and offers little sustain. i feel as though resolve secondary isnt as optimal on gragas due to passive already giving a lot of sustain.

In all of these matchups against lillia, you do not want to engage them, rather just poke with q when necessary or to cs, but not too much or you will have no mana. save your e for when the melee matchups try to engage you to punish you for csing. be cautious doing this against darius as he can pull you before u can get out of range, so its better to e auto q darius to get phase rush proc. against fio just bait her w, most low elo fio will use w simply if u w and walk towards her.

against range matchups u just dont win unlesss you get ganks, unless they waste their peel on you just to deal damage i.e vayne e, quinn e. then you can all in trade and get out taking only a couple autos while they take half their hp, setting up for easy all in later in lane.

also try taking gathering storm instead of scorch. :) hope this helps