MAK,
I am 47 years old, Type-2, have HBP, and have a stent in my heart, so I'm on the same meds as you + more. I have lost weight over the past year, and have my HBP and blood-sugar under control, but am still on the meds. My doctors will ween me off of some within the next 6 mos. or so. A few I will be on for years, maybe life. I will be getting off as much as I can, as soon as I can, but not until the time is right ... I'm not pushing it. It will happen.
To your point ... I take metformin (glucopage) twice a day, and glipzide (5 mg.) for my diabetes. Lysinopril for HBP, and Coreg (beta-blocker), aspirin and Plavix for my heart. And, Lipitor for my chloresterol. I was having similar problems with my stamina, and sore aching quads. Not sore muscles after a ride, but I felt like there was an excess of lactic acid in my quads all the time when riding, even on an easy ride. My doctor cut my Glipizide from 10 mg. down to 5 mg. (because I started to have alot of blood-sugar crashes). Now, I don't seam to have the soreness in the quads. I also take it at night now, instead of the morning, so my sugar doesn't crash after my daily rides like it used to. I know the Coreg (beta-blocker) is what is causing my stamina problem as it has lowered my metabolism (losing weight has been slow), and I don't always feel like riding hard. What I do to combat that, is drink either a cup of green tea (caffeine) before I ride, of use a GUE gel with caffeine before I ride. Recently my rides have been MUCH better, and more enjoyable. I'm not sure if the metformine actually affects my riding, since the aches in the quads have seamed to go away since I cut the glipizide dose and changed the time I take it. All I know, is that for me my rides have gotten better.
The next thing to get off of is the Lisinopril for the HBP, since I can't get off the beta-blocker anytime soon. I figure getting off the BP meds will help me get my metabolism back up to speed. At least closer to where it should be. Right now, I haven't been able to reach MHR no matter how hard I try. The Coreg just keeps my heart working so slowly ... my HR is around 60 (when hanging around the house), while my BP has been around 110/60 (even lower after my rides). When I ride hard I can't get my HR above 145, no matter what I do.
I have no problem riding long distances (150+ miles/week), but I do fatigue sooner than I used to before I got fat and sick, and had to come-back from the dead. Now, I pay very close attention to my hydration, and fuel intake. I have recently completed a VERY hilly century and had NO problem with my hydration, or my fueling. My sugar is fine on long rides, but I have to keep up with my sugar levels after the ride to keep from crashing (not as bad lately).
What I have found ... some prescription meds affect your cycling, and some don't. The bottom line, is that by paying attention to your bodies signals, and being aware of what meds you are on, you can keep the problems to a minimum.
By asking your question, you have taken the correct first steps. Good luck.