Late period confusion

Natalie • I
So I am 18 days late. I don't believe it is pregnancy. I am very tired and have been having horrible mood swings, but I'm also very depressed and my allergies and sinuses are bad. I have been gaining weight and it's hard to lose it. I'm trying to see if maybe it would be PCOS. Any comments for advice, I really need some right now ☹️