4 months PP and possibly pregnant...?

Hello, I am 4 months PP, I am exclusively breastfeeding and I took a pregnancy test today and I have a very faint line.

I'm a little nervous because I didn't think I was going to get pregnant this soon after having a little one (especially since it took a little over a year and fertility treatments with the first one).

I wanted to know if anyone out there had babies back to back, and what happened to your milk supply? Also how was it getting back into shape after 2 babies in a row? And this might be a silly question but health wise will I be okay? Lol