I had that happen around that age. Smoking weed caused me to have some grandiose realizations. When depressed, those realizations become infinitely dreadful. I feel you, and I hope you take a break from weed.

You might just get over the thoughts. If you are still suffering after a few weeks, make an appointment.

The point of life is not something you can ever figure out. It is an endless pursuit of an elusive answer. Existential thoughts are broad and rudimentary. We tend to simplify things. I don't believe things are that simple. All or nothing, black and white thinking is destructive. Things aren't that simple. Obviously you feel that this is an absolute truth, that living is pointless and there is nothing more. There is more. There are more things to feel.

From my experience with mental health professionals, I have found that they don't care about the nature of your existential realizations. They care if you have symptoms of anxiety, depression, or mental illness that they can identify and treat. They don't care about the meaning of life or how everyone is a blind sheep in a cosmic slaughterhouse, mannn, etc.

Don't get dependent on weed. It is shitty when you want to smoke weed to feel normal. It's not normal, it's stoned. It makes you forget your pain. It makes you comfortable with the thought of doing nothing and feeling ok, which is good for recreation and relaxation. It doesn't help you move forward with your life. It doesn't help you learn or develop in healthy ways. It will deteriorate your memory and your patience. Your social skills will suffer. You may slowly lose the ability to cope with daily stress.

Don't be me, 9 years later doing the same thing, having the same depressing thoughts, thinking about how many years I gave to pointless angst, still smoking weed as a mental crutch. It has therapeutic effects but it is not fit for treating anxiety or depression in my opinion. It only pushes it under the rug.

Sorry about going off on weed. I love weed. I'm afraid you might smoke it again, feel good, and see it as a cure for your symptoms and continue using it in that way like I did. It doesn't work.

"See a therapist" seems to be the most general answer to these anxiety posts, and it's probably good advice.