Your form is actually pretty good for someone who's only been lifting for a couple of month.
The only thing I would suggest is to drive your elbows down and keep your lats tight.
You said you decreased the volume to 3x5; just remember, volume and intensity have an inverse relationship. If you're doing less total reps (15 in this case), the only way to get stronger is to increase the intensity (weight used). Otherwise I would go back to doing a 5x5 and just lower the intensity to something that doesn't bother your joints, and work on building up your work capacity.