Service upgrade or sub panel?

Hi there everyone, My question is about how to add a hot tub to my panel that is maxed out on breaker space. I have a 200 amp main GE panel(quad breaker) and I am currently pulling 100 amps on one leg right now. I have a tankless water heater, 3 A/C spaces and another 2 water heaters. Square footage is 2800 if you need that. I will be posting pics here shortly. Thank you. Let me know what other info you need? Do I need to upgrade service or can I just add a sub panel?