Miscarriages

I've been with my fiancé for about a year, we have had 4 miscarriages throughout the year we have been together. I have Hypothyroidism I found out when I was 16 & have been taking my levothyroxine for my hormone levels since I had my second miscarriage my dosage has gone up. It's been so hard to have baby & discourages me to even try most times. All I've ever wanted was to start a family, my fiancé has 2 kids from his previous relationship. I don't know what to do anymore, sometimes I just wanna give up!