I feel sudden influxes of sadness and often times it’s really irrational. I know it’s stupid, but I just feel so SAD, my heart hurts and I just start crying uncontrollably I also have thyroid issues ?

I don't think thyroid problems have anything to do with this.. But it does sound like depression. Sometimes something traumatic can trigger it, or it'll come on its own time. If this continues and or you have suicidal thoughts, consult a doctor or a therapist. Talk to someone you trust. Don't keep this a secret and definitely do not keep your emotions bottled up inside.