Diana mid is a burst caster, meaning that all of your damage will be coming from your q and r, maybe a little from w and your passive. Get rid of all things resembling attack speed or bruiserish items. (frozen fist, aspd marks, trinity force.

You are a melee mid, so you will be taking considerable poke from your opponent and from creeps. armor seals are a must.

sorc shoes > zerk greaves ALWAYS

I also don't think athene's grail is very good. You aren't reliant on cooldowns like mages that need athene's, like veigar and orianna. Change those things then pm me.

can you give me more information about the mess?

What a mess.