Recently I've been getting a lot of physics questions, and I'm at the point where I'm asking a couple a day. Should I restrain myself, or can I go willy-nilly as long as they meet the standards of the site?
There is no rule against asking too many questions. More questions make the site better. If you have three questions today, ask them!
There are, however, rules about asking too many low-quality questions. And, because writing and being creative is hard, users who ask a lot of questions frequently start having trouble asking consistently high-quality questions.
I use this data.SE query for identifying people who write lots of questions and answers (beware that the column names don’t change when you switch to questions). For the week ending 2021-10-31, which is the most recent available, you were in fact the top asker on the site, with seven questions. For the month, with nine questions, you’re in the top ten or so. But we had 2653 total questions in October, so your nine make up about 0.3% of the month’s questions for the site.
From having used that query for several years, our most active askers tend to cap out around one question per day, and our most active answerers tend to cap out around three. Some people will do more for a burst, but people’s activity level on the site tends to ebb and flow.
As long as your questions are attracting upvotes and answers from other users, feel free to ask more. If you start to get negative feedback on your questions, such as downvotes, close votes, or comments suggesting improvements, take that feedback seriously.
Note that some SE communities do punish asking to many poor questions (i.e., questions that do not get any upvotes) by limiting the user to asking no more than one question in a specified period, e.g., half a year. Although they give one the possibility of editing one's old questions (potentially completely rewriting them).
I don't know, if PSE follows this practice.