Friends always asking

My husband and I have been TTC for about 5 months now. I'm not too concerned that we are not pregnant yet (of course I wanted to be yesterday!). I have just started to seriously track as of 2 moths ago. Anyway,  I'm 32 and many of my friends have 2 or 3 kids already.  How do you politely answer the question "has it happened yet?" Or "are you pregnant"?  I simply answer no every time, and receive their words of sympathy (which doesn't help) but it's almost like they don't understand that it doesn't just 'happen' for some....