There is a concept often talked about on Thunders Place called "Physiological Indicators," and it's meant to help prevent injury. These indicators are "signs" or "sensations" that something isn't right. Don't over exert, and frankly, if your penis doesn't respond well to an exercise, tone it down or discontinue it altogether. We're all built differently, including our penises, it's important to listen to our body's guidance in this regard.
Many of us are performing these exercises without medical supervision or clearance. This is why being cognizant of your body's reactions are so key to success or failure. Maybe this device and/or exercise isn't the best fit, especially given your description of the situation. Or maybe tone it down considerably, to like 10-15 minutes at a time. I believe 90 minutes is a lot of time if you aren't experienced.
Personally, I don't recommend these exercises without medical clearance or supervision (like for example, after a ligament surgery), and if you are to perform them, start ever-so light & slow. I look to try pumping again soon, and I too will be on the lookout for physiological indicators.