Ttc

My fiancé & I have 3 girls between us from a previous relationship, we've been trying to conceive for nearly 2 years now & still nothing it gets me down when I do a hpt & its negative I can see that it hurts him & I feel like it's my fault I/we haven't got pregnant yet I feel like I'm letting him down were desprite to have a child of our own, we bought conceive plus to help us after seeing so many success stories but we haven't been successful at all.. We've recently started planning our wedding to keep our minds off Ttc in the hopes that not being so wrapped up in babies that it would just happen.. It's getting me down,everyone around us is pregnant & Im left to feel like why is it not happening to us.. I'm 24 & he's 28 so we're still young & shouldn't be having so much trouble Ttc.. It knocks the heart out of us both because he gets excited & I have it in my gut that the hpt will be negative & i can see in his eyes he's disappointed but he tells me it'll happen baby don't worry.. we just want to extend our family & have our own little one together he is such an amazing daddy/step daddy & I love him to death. we both wanna see a doctor but putting it off I think in fear incase we are told something's wrong.. We're mad about each other & he's said about IVF if it comes down to it but I think it's to expensive & not garanted to work.. Is there anything we can do? We've done the pillow benethe me & all the others plus conceive plus..