Depression over TTC

Deanna • 27 years old. Teacher.
My husband and I have been TTC for about 4 months. I feel like I'm doing everything I should be doing, but it's not happening. 
I have had 2 late periods over the past 2 months and have been devastated to get negative tests and then get my period.
I feel like I can't control my body any more and I think I'm becoming border-line depressed. I think about being pregnant constantly. I get sad when I see pregnant women and babies. 
I don't want to feel this way, but I can't help it. Any advice?