Hi ryan, I'd agree with maybe your doctor or a T.
But maybe you need a little support with what's triggering that sadness for you too.......with the nostalgia maybe that's a sense of loss, maybe grieving the loss of something/someone/times in your life..........??? And grieving can be real tough at times, if you want to talk about those memories/your feelings with us.........
And/or maybe there's something missing from your life right now, which makes those feelings a lot more intense?? Could be anything......connections with others, feelings of security, plans..........maybe things you could work on developing more........to make the "right now", something that may compensate a bit more for those "times gone by"???
Just some thoughts, if you want to talk a bit more about what's going on for you.........

Alison