Don’t know how long I can do this!

I have 1 child a son who is 9 years old. I never really thought bout having another baby, but in October 2016 I got pregnant just after my wedding & had a miscarriage without even knowing I was pregnant. Since then I have wanted another baby so desperately but it’s just not happening, we’ve been trying for over 15 months & noting is happening. We’ve both had tests at the doctors & there isnt any fertility problems so I don’t understand why I’m not getting pregnant. Due to this I have suffered with really bad depression & even started self harming. I’ve seen a councillor about this & I have been getting better. But every month when I come on my period I feel like I wanna die. I seriously don’t know how long I can go on doing this to myself. My husband is desperate for a baby & so is my son it makes me feel like such a failure. I don’t know how others go on!