what caused me to get thiroid at 18 years old?

I was 197 when I got pregnant and I got the Gestational diabetes then when I was send to get indused at 38 weeks my blood presure when insane .. when I was stending up it would elevate to 179 so they layd me down in the bed and it would go to 90s I was resiving oxitocin and my labor fail I never dialate so I end it up with c section .. (im a huge baby when it comes to needles) I have anxity and I was terrified of the needle in my spine then the whole proses I was chacing scared when I was done with my c section they took me prospurtum (I think lol) thats when my pulse when crazy elevating to 200s and I was feeling fine .. they took me away to the ICU away from my baby I couldnt brestfeed for 1 week they put me on monitors to check my heart they put ink in my blood to check agien and after 4 blood test they came up with thiroid? I got discharged and I lost in 2 weeks about 40 pounds proping to 203 im never hungry and brestfeeding is out the question thanks to the ink .. what coused this