Ttc for 7 months

Me and my fiancé have been ttc for 7 months ! We’re both 21 I’m not a drinker I have never done drugs and I’m healthy . I am a healthy Weight and I just don’t understand! We started at the end of dec 2018 and we had a miscarriage/ chemical pregnancy last month. I was 4 weeks pregnant got lots of faint lines same day I went to do a blood test I started bleeding . Doctors said I lost the baby. I don’t understand I’m young healthy and having such a hard time . When I go to my gyn they look at me like I’m a child and won’t help me in anyway Tell me I have to try for 18 months befor they will do anything . Ugh. What should I do!?