I need support ladies :(

My husband and I have one beautiful 5 year old daughter who has been begging for a sibling for the past two years. We have been actively trying; not using contraceptives of any kind, waiting to have sex during peek perdicted fertility etc. To no avail. For reasons unknown I've had extremely irregular periods and now my ob thinks it's time to see an infertility specialist. I'm 28... and heartbroken. Any similar stories or words of advice?