Why is it taking me forever

Why is it taking me forever to get pregnant? It's been 9 months of TTC and nothings happening. Its hurting me so much. I want a baby and this is the last month I can TTC because my husband is getting ready to leave for training in the military and will be gone for 4 to 5 months. He will come home once a month or I will go there sometimes but that's probably wont be when I am ovulating. This is hurting me every month the test comes back negative and then when my period starts. I hate the feeling. I just want to get pregnant and my husband gets upset every time to because he wants to have a little baby boy.