In a chemistry lesson in school one day, I was forcing a glass tube through a holed rubber bung with some force. Glass tubes and twisting don't go well together -- The tube shattered in my hand into about 6 pieces and the pushing force I was applying buried a small shard of glass deep into my finger. I pulled it out and it bled heavily. Much numbness as well. Maybe it caught an artery? I have a scar there now. If I press and wriggle it, it sometimes stings. I have often wondered if some of the glass is still in there.
[puts on Minor Injuries hat]
It's probably unlikely that the glass will have remained embedded in that wound for all that time without the wound becoming inflamed. If in doubt, you could get it X-rayed for peace of mind, as glass fragments usually do show up on wound X-ray images.
It's probably more likely that the original injury damaged some of the nerve endings, leaving a small patch of hyperalgesia (increased pain sensitivity) which could also account for some of the numbness initally. You can try something like ibuprofen, or alternatively ask your doctor for specific neurogenic painkillers if it becomes a bigger problem. (Pain is a very subjective thing clinically, and many people have different tolerance levels of pain, although management largely uses the same biochemical principles.)
[takes off Minor Injuries hat]
I remember another small injury, when I took a fall during gymnastics at school, and landed on my upper back. It knocked the wind out of my chest for about 10 minutes.