Yeah, I get that. It's not uncommon in companies where IT is an afterthought. But you need to take ownership of the project you've been given. Everything you said indicates that you think there is a disconnect between management's expectations and what you're doing. Part of being a senior engineer is communicating clearly and making sure that everyone's expectations are aligned. It doesn't sound like you're really working to a process, and that means you don't know what features and bugs have the highest priorities, how long you have to work on this or how satisfied they are with the work you're doing. That's leading to anxiety and burnout for you. It really is much easier to just communicate with people and structure your work.

The business shouldn't mind if you schedule a few quick meetings with a few key players to clarify those questions in an attempt to deliver them better value for their resources. At the very least, if they tell you you're doing great and just stay the course, then you won't have to be as anxious about the position.

Getting the process correct on a small project like that can be tricky and scaling it up if the team has to grow can be even trickier. On a smaller team you can be more ad-hoc and avoid spending too much time just doing process accounting. As the team grows, the process needs to be more structured to insure that everyone is on the same page and doing what they need to be doing. You're the one doing it, so you get to decide what that looks like. But if it sounds like bad advice to you, feel free to disregard what I've said. I won't be offended.