On the verge of giving up

My Husband and I have been ttc for 4yrs now. We both have children from previous relationships but so far have had no luck what so ever. It seems like we have tried everything. We're too afraid to find out if we are un able to conceive, basically get tested for infertility. I joined glow so I can start tracking better for a year now and still nothing. Any advice or any pointers would be much appreciated. Unfortunately sometimes we have to be away from each other for 6mo to a yr due to his military career so there has been 1 gap so far out of our 4 yrs of trying. After planning for a while we gave up and said it will happen when it happens but every time I get my monthly woman visit I just get more and more upset. I feel like it's getting completely hopeless but I know deep down with a little help and support maybe just maybe we will get blessed with a miracle.