hi good afternoon my boy is 9 months completed and now in 10th month , he had 4 upper teeth and 2 lower teeth, now in upper 5th has been generating, he keep on keeping his lower lip under the teeth so that the lower lip was swelling and some part blood was slotted I guess , because it is showing in black colour on the some part of lower lip, so is this common behaviour? if not please suggest thank you so much