Starting to Feel Discouraged

My hubby and I are ttc#4... Our first baby wasn't planned, # 2&3 were both planned and it took us 4 months to concieve #2 and 3 months for #3... We've been trying for 10 months now, no success... I know people try for much longer before they get a positive...... But it's taking so much longer this time than it did before. I'm starting to feel really discouraged, and I can't help thinking maybe something is wrong with me... I'm sure I'm just being silly about that but still can't help to think it... Any other mommies out there have a kid or 2 easily and then have a harder time getting pregnant?