Feeling miserable

I am 27 and my hubby is 28. We are ttc since 6 months and no luck. Everytime my period comes i cry because i feel incomplete and hopeless. I have a 2 year old son. I got pregnant after 3 months of trying. I tried everything agnus cactus, pre seed, concieve plus and ovulation kits. I feel hopeless and sad. All my friends have two or three kids. Some if my friends are pregnant and i feel left out. I really wanted to give my son a sibling because i am an only child and hate it. I am fed up now and dont know understand what the problem and and feel like giving up now. When  should i see the doctor? I feel like giving up and deleting all these fertility apps.