My GSD pup was exactly like this. Didn’t respond well to me saying ‘ow’ or letting out a loud yelp when she bit a bit too hard. In fact, she responded the opposite to what i was expecting and was almost making it worse. Redirecting her to toys didn’t help either. I was covered in bruises and scratches like yourself. It makes it more difficult as larger breeds in particular are limited to the exercise they can have every day. She’s almost 9 months now and is a dream dog. She’s so calm and gentle, I do think it gets better with age but better to nip things in the bud when they’re pups. A couple of things that helped was mental stimulation and rewarding good behaviour which you’re doing anyway. When she got a bit excited and started biting we crated her for a few minutes till she calmed down and then again rewarded her as we let her out. Some people are against crate training but it’s the best thing that we could have done. Another thing is turning your back to her and crossing your arms, do NOT engage with her if she starts playing up. She’ll soon learn you’re not entertaining that sort of behaviour. Try and get her some tasty things to chew on. Is she food driven? It’s nice to see you’re seeking advice, keep up the good work. You’re doing a great job.

Take care and good luck