How do you stay positive? Please help

After 4 years of trying how do I say positive on a day basis I feel like once a month I get a massive wave of depression when I take that test I need some tips on how to be positive.

In the beginning and I was positive, upbeat. I'd tell myself it will happen but as the years went on I just couldn't keep it together anymore, family members would start having babies and then they start having their second babies and I'd still be in neutral. I am 28 years old... time is not on my side

Any positive advice I will take