Why am i feeling depressed?

The past few months i've been filled with anxiety and its been hard to cope but i managed it just fine. Now starting last Friday the anxiety shifted to depression. I just finished school for the year so i should be feeling a sense of relief and ready to enjoy 3 months off from school. But im feeling a strong sense of pessimism. Anytime i remember a memory from the past rather than looking at it with a sense of happiness i feel nothing but sadness wishing i could return to that moment when i wasnt so miserable.

Exercise isnt helping me, talking about it isnt helping, spending time in the sun isnt helping....i dont know what to do. I really dont want to feel this miserable for the entirety of summer...