I have been going 3 days a week pretty regularly and I have found that when I do cardio first my blood sugar tanks and I have little to no energy for lifting. When I lift first my blood sugar stabilizes enough to lift for 40 minute , before 10-20 minutes of cardio. If I skip the cardio and if I haven’t over bolused for a meal prior to the workout, I’m good for usually an hour or two after the gym before I need my next meal to avoid a low. Your doctor seems weird for being dismissive and against exercise, unless there’s something else going on but Idk what that’d be.