This is the time of the year for it to flower. Read up on growing it to find out when to plant for longest term of usable foliage.

Get new starts later in the year. I plant in Fall and always have plenty over winter and in early spring.

I have had Italian (flat) parsley self-seed in my garden. Just don't mulch that area and keep an eye out for seedlings next spring.

I have never had the curly kind self seed, but I have grown it from seed. It wasn't difficult, but germination is slow and irregular.

Have you watered it?
I have planted parsley in two places this spring.
In one place i water and cut and it's growing nicely.
In another place (i forgot about it) it started to flower.