Well without seeing the wound it would be hard for anyone here to make good recommendations. I recently injured my finger resulting in several deep gouges out of it. I used these and they seemed to help a lot.
http://www.cvs.com/CVSApp/catalog/sh...new_crumb=true
In general keeping wounds moist makes them heal better/faster with less scarring. Letting them dry out makes for painful scabs, and prone to picking, thus delaying healing. Keep them moist and covered is the better choice.
But as a diabetic, if your wound is already 3 weeks old, and not healing (or just slow to heal due to depth or size of wound?) you should probably consult a medical professional. Do not mess around with this. GO. TO. DR. I know too many people that have lost toes and/or feet due to this.
My experience with pharmacists is that they are very familiar with Rx drugs, but no so current or knowedgeable on OTC offerings. YMMV.

