tingling in lips, painful, uncomfortable feeling / excessive salivation

Can someone please help me with this problem?
I've been having a tingling, prickling, pins-and-needles kind of feeling in my mouth, mostly in the region around the lips. It gets worse especially when I'm stressed, like during an important test. When I relax, it recedes a bit, but it's still there. Also, it's harder to talk because my lips feel really stiff and I think I've been having more salivation than usual, so I'm afraid of spitting when conversing with others. This has happened for more than two years.
Is it something about my nervous system, or is there some other kind of cause to it?
I'm don't think it's a problem with my teeth (I had my braces removed seven months ago, and am currently wearing retainers. I'm still a teenager in high school.)
Thanks in advance. This means a lot to me. I've asked many people, including my family doctor and dentist, but they brushed aside my questions because they assume that I'm just overthinking it. But recently, the problem has became painful, and sometimes there's an uncomfortable, burning feeling within my lips. It has become very bothersome and infuriating to deal with. If someone can help me with this problem, I will be very grateful.