Can a 3mth old be teething?

It's possible! Although most babies start chewing and drooling at around this age and don't start cutting teeth for several more months it's possible for teeth to start coming in now. In fact, sometimes a baby can be born with one or more teeth! thankfully, that's rare. If you look at your baby's mouth and you see one area of gum that's red and swollen, and you feel something quite sharp underneath, it's a tooth!
Possible. Although the milk teeth develop when the baby is growing in the womb, the teeth only start to grow throughout the gums when the baby is 6-9 months old (although it can be before or after these ages).
Unusual. But can happen. Baby teeth begin to develop in the womb, but usually don't begin erupting until 6-9 months. Baby may exhibit, teething behavior (drooling, fussiness, hands going to mouth, irritability) at any time. Give baby chilled teething ring and see if that helps. The moment 1st tooth erupts make appointment with Pediatric Dental Specialist.
Yes. Teething is a normal physiological process as teeth erupt. The average age of erutption is 6 months but can occur as early as 3 months. Mild symptoms that gradually improve usually are nothing to worry about and may even be related to a viral infection or other condition. Severe or ongoing symptoms should be closely watched and discussed with your pediatricia.
Yes. It is not likely, because it is rather early, but it is possible. The first teeth (lower front teeth usually) often appear at around 5-7 months.
Possibly. Very unusual. Most 3-4 mos old drool, put hands in their mouths and exhibit " teething" behavior. But it may happen.