RoughCoronet0
Dragon Lover
It wouldn't be too hard to have Swarmkeeper fit thematically if you lean more on you fey connections as one of the example options for the swarm's appearance is playful pixies. Maybe your time serving Iggwilv eventually manifested an ability to summon your own little swarming minions. Maybe they are there to keep an eye on you for their true fey master, or maybe they prefer you to their previous master.Swarmkeeper would be good mechanically, but is going to be difficult to work thematically.
You could also easily reflavor your swarm into draconic fiends of some sorts to better fit your connection to Tiamat. Maybe your service to the Cult of the Dragon and to Tiamat has granted you favor in the goddess's eyes and she grants you the secret to summon your own minions, like a swarm of pseudodragons or draconic imps.