thought id give my take as someone with pdd and anxiety here whos been medicated for 5 or so months now
i was totally new to medication as well, when finally went to my doctor about getting something prescribed for my anxiety (i have agoraphobia and gad) she prescribed me the ssri sertraline as i had mentioned really low moods that have been persistent for years and years as well.
i take 50mg daily now, it took a while to feel any effects as it is an ssri, but 5 months in my anxiety has definitely significantly improved. because of anxiety i used to not be able to post on forums despite being anonymous for the most part, shake before messaging friends, constantly get racing thoughts, panic attacks, and be brought near to tears when outside but i dont have any of that now. i have been taking the train to school everyday recently and i went out with friends for the first time in over a year a few days ago. i still get 'anxiety' in situations to some degree (and because ive been doing new things that ive avoided for years) but im able to deal with this better now (hell its a miracle i can even say that with the state i was in before) best way i can describe it is putting down some notches of difficulty, it just made it a lot more manageable for me. its not a instant 100% anxiety block but i dont want it to be, i was scared it would completely numb me- but thats not the case with the dose that seems right for me now, and im able to feel like im playing a role in my recovery as i have control still.
as for pdd it has helped with that too a bit, im not constantly sad and easily set off into spiralling into self harm and suicidal ideation on good days (im so relieved i can say i have good days now, where i hadnt for over 4 years before medication) i still have bad days but they are less frequent than daily lol. theres still more than a normal person would get but its manageable now.
i really recommend getting on something, i think i was really lucky having something that helps in the first thing ive taken- but if this is not the case for you please dont give up with medication because when you find something that is effective its really great.
hope this helps a bit, wish you all the best :)