beet juice for long streangth training sessions?

When I was a hard core triathlete I used to eat Power gels and drink Gatorade mixed with a little whey protein to make sure I didn't run out of energy during long workouts. Now that I'm training in Olympic Weightlifting and the weights I'm lifting are getting heavier its taking me longer to complete my workouts, and now I'm struggling with fatigue the later part of my workout. Rather than trying gels and Gatorade again I decided to try some fresh beet juice mixed with a little whey protein. It worked ok. I still had a little fatigue by the end of the workout, but not nearly as bad. The problem I had was by the end of my training session my stomach was upset. The stomach ache stayed with me until the next morning. I'm hoping it wasn't the beet juice that upset my stomach, but me drinking a combination of water, beet juice/whey protein and coffee- yes I drink coffee when I strength train. Coffee while training is something I started doing a decade ago, now I just don't feel worth a darn while lifting unless I have a hot cup-o-Joe to sip on in between sets. On Saturday I'm going to try the whey/beet combo again this time without the coffee. If I complete the entire workout without fatigue or a stomach ache I'll know beet juice was a good idea. If I still get a stomach ache then I'll know I need to switch to Power gels, Gatorade with whey protein, and yes of course..... coffee.