Keep lifting. Do lots of good mornings. You should LIVE on good mornings at this stage.
Additionally, do a lot of static stretching on off days and dynamic stretching on lifting days.
Also, get acquainted with ART, someone to give you massages and the foam roller, as they are all part of the equation when considering flexibility.
This is a situation where you have to bite through the pain on the stretches, but don't take that as an invitation to lift weights you can't handle with good form. Use your best judgment here.