This is quite difficult time for your toddler, at this age there must be eruption of deciduous first molar going on which causes irritation, increased salivation, pain etc. Biting on cold teething toys kept in freezer might relive some pain. Biting on cold carrot, cucumber etc might help but cut piece might choke. Syp. Paracetamol SOS can be given but not more then recommend dose.
Next Steps
Consult a pedestrian or Pedodontist.