condoms ?

I took the pill for 8 months and it led my thyroid to become imbalanced and now I have hypothyroidism. Só I decided I would stop taking the pill and any hormones. From now on I will only use condoms. But I was reading online and it said that 18 out of 100 people get pregnant with condoms and it scared me. I am thinking of having the non-hormonal coil but I'm slightly scared. 
Can I really get pregnant relying only on condoms?