I (as my 13-year-old son) bit my lip and now there is like a light grey lump inside of my mouth (behind my lip). i can feel the lump with my tongue?

Well you are young to be participating in such an adult forum, well done. You have probably cut and blocked the duct of a salivary gland in the lip and now you have a mucocele, a collection of mucous in a sack. Have your dentist look at it and advise you what the best thing to do is. Resist biting it!

Avoid playing with it with your tongue. Avoid biting it. Be careful eating the next few days. It should heal, like any other bruise, in a week or so. If it does not heal then see your dentist

Agree with Dr. McLeod. The child probably has a mucocele and it may require attention of a dentist or oral surgeon. Visit this site for info: https://medlineplus.gov/ency/article/001639.htm Wish you and your son good health!

The bite may have damaged the duct of a minor salivary gland creating a mucocele (radula). It should self resolve in under 2 weeks. If not, see an Oral Surgeon. Healing tissues sometimes appear grey. If not completely resolved in 2 weeks, see an Oral Surgeon.