Hi and welcome @Blah!

I have also dealt with mental health issues that were linked to boredom, or lack of intellectual challenge/stimulation. There is an array of resources on mental health and giftedness here that were recommended to me on that forum, and have been helpful to me: https://www.davidsongifted.org/resource-library/gifted-resources-guides/mental-health/

I wouldn't say it is necessarily "common" or "uncommon" to encounter this type of problem. Any individual is unique in his/her reactions to the environment. As you go through these resources, you will see that some characteristics of giftedness might have been involved in the etiological process.

In my own path, I came to understand that mental health issues are complex phenomena with a wide array of causes and contributing factors; importantly, not all need to be related to giftedness. So I would personally encourage you to try and understand, as best as possible, which those factors are in your specific case. Personally, I went about this trying to disentangle what was linked to giftedness and what not; making this distinction was quite helpful to me in the process.

Concerning the "tedium" of undergraduate studying that you mention, I will throw in a few ideas:
1. Get involved as a research assistant. If you are proactive about it, you might soon enough be involved in intellectually more challenging projects
2. Create your own challenges. Universities are also a place of self-directed learning; if you have topics in which you want to dive deeper, go ahead and do it! If you have (at least) decent educators at your university, having more (or different) input than usual from a presentation, or an essay, will be appreciated. Furthermore: maybe you can do a double degree? At least add some more classes? Complete the degree in less time than imparted? I believe, you have more freedom at a university, than in high school
3. Look deeper into yourself and try to understand why you are doing the degree; for example, if you believe you are interested in research, then yes; unfortunately you need the undergraduate degree in order to do a PhD (as far as I know - my knowledge of US education is limited, I am in Europe). A short-term struggle can be necessary in order to reach a long-term goal.

Concerning your assessment, and descriptions of the level of abilities as a child, I honestly do not know - I believe others on the forum are more versed in these questions than I am.

Wish you all the best!