I can speak to the Niaspan and Aspirin - no worries with them. I take 3000 mg of niaspan, plus the 81 mg aspiring with no adverse affect on riding. I've no idea about the others, but some here have addressed them. I would concur that other heart/blood pressure drugs (toprol/metoprolol, altenolol) can definitely do it. Metoprolol held my heart rate way down - 40 resting HR and my initial dosage (50 mg) made me a sleepy sack of coal. Altace doesn't affect me, but it has done the same for a friend, but you don't indicate taking any of these.
The Niaspan is well know for causing flushing, but usually only short-term - a few hours. Take it before bed to minimize issues from it.
It may simply be the need to build up more endurance on climbs - I still can seem to wear out on climbs, but I'm better than I was and am developing better technique (lower gears).