Deadlifts will almost always bring on soreness but there is a fine line between muscle soreness and muscle strains/pulls/tears.

Sounds like you may have a strain but it's hard to diagnose over the internet obviously.

When deadlifting it is absolutely crucial to keep your lower back locked. Your lower back should not round over ... if it does you WILL get hurt.

I've struggled with this but you can get around it and get stronger it just takes knowing your limits and knowing what good form really is/feels like.

IW