Frustrated

My husband and I gave ourselves a very small window to conceive due to our ages. We just got married in March and he already has two children and I have one biological child. I am 39 and he is 37. I want to get pregnant by my 40th birthday but we are not having any luck. We have been trying for five months now and I have had lots of pregnancy symptoms but it's always negative test and periods. I'm at the point where I just want to give up because it seems like I am forcing us to have sex. 😭 I just want another baby so bad. I never wanted my daughter to be my only one and my clock is ticking so loudly it is giving me a headache. Please sprinkle tons of baby dust on me. I'm feeling defeated.