The two medications you mentioned serve me well. I have Ativan as a prn, but it's one I rarely take, nowadays. But it does indeed help with situational anxiety! For longer-lasting stress/anxiety, some extra Seroquel prn (or an increase in my base Seroquel XR) has worked great.

I take 600 mg of Seroquel XR (generic) daily, at night with 600 mg Tegretol XR (generic). Each morning, I take 100 mg generic Lamictal. When I mention Seroquel prn above, I refer to my supplies of the instant release (iR). As a prn, I might take between 25 or 50 mg a shot, up to 150 mg total in a day (beyond my base XR dose), but that's only when mixed states, or similar symptoms, are brewing...or sometimes even for anxiety, which it does help curb.

Insomnia:
If I can't sleep on the 600 mg XR, generally the extra iR small doses do relatively little to help. I confess I then might add a 1 mg Ativan as a booster. Maybe being a totally different med makes the extra difference? I know small doses of Seroquel iR help many people sleep, though.

Low Energy Depressed:
If I'm purely depressed, prn iR may or may not help during the daytime. Often lowering my base Seroquel XR does more good for that, taking me closer to the recommended 300 mg for depression control vs. higher doses for mania control. If anxious during the day, I tend to choose Ativan for anxiety since unlike at night, it doesn't sedate me during the daytime.

Mixed Mania or pure Hypo or Mania:
If I am high energy in any way, the Seroquel iR prn is the best choice. That or an increase in my base XR. The added amount won't usually make me tired. Just "Coooooooooool Jaaaaaazz", at the most. Or stabilization. Ativan does little for my mania, unless I take a huge enough dose, which I wouldn't. It has been administered in larger doses in injection form, in the psych hospital. That's for the nurse/doctor to do. Not me. At high doses, Ativan will knock me out during the day,

Really, it's something you'll have to feel out for yourself.