The best way to feel motivated is to know why you want to get something done.
The most motivated (and productive) people are the ones who constantly question why they're doing what they are doing.
When you focus on doing more things, as opposed to doing things that are aligned to your values and what you believe in, you may be able to push yourself to be productive in the short run, but in the long run you're going to be a lot less satisfied and productive. The key is to determine what you value and what motivates you the most, and then take on tasks and responsibilities that fit with your values.
Just because you're constantly busy and you produce a lot doesn't mean you're productive—in fact, I'd argue that the opposite is the case. Productivity isn't about how much you do, it's about whether you achieve the outcomes that are the most important to you.
When you always know why you're doing something, you're going to be a lot more motivated and productive.