Gummed it up with the stop leak or the therm is bad.

Pull the therm out and drop it in a pot of boiling water if you see the spring move it’s opening and good if not replace it. Also bypass the heater core to rule out that as a clog.

I’d also be checking the block for any freeze plugs considering we just came out of winter and u said hit a bump got a leak. Kinda sounds like a freeze plug but that’s just a guess.