Oh, it's my turn can't miss that !
Anyway "OH" is a nice word you can use it in all situations :
Oh, sorry I stepped on your foot
Oh, what a beautiful bouquet
Oh, this is really disgusting
Oh, you make me so happy
and to facilitate your choice with letters starting with an "O" here a some examples :
overgloom, overgo, overgoing, overgone, overgorge, overgrace, overgrassed, overgraze, overgrazed, overgrazes, overgrazing, overgreat, overgreatness, overgreedy, overgrew, overgross, overground, overgrow, overgrowing, overgrown, overgrows, overgrowth, overhale, overhall, overhand, overhanded, overhandle, overhands, overhang, overhanging, overhangs, overhappy, overharden, overhardy, overhaste, overhastily, overhastiness, overhasty, overhaul, overhauled, overhauling, overhauls, overhead, overheads, overheaped, overheaps, overhear, overheard, overhearing, overhears, overheat, overheated, overheating, overheats, overheavy, overhele, overhent, overhigh, overhighly, overhip, overhipped, overhipping, overhold
Have fun !