A.C.
My sympathies. I've suffered several miscarriages myself and completely understand the feeling of loss. After my last one, I chose to wait nearly a year before trying to get pregnant again. I needed time to grieve and become mentally and physically healthy again.
25-28 days isn't so irregular...but you need to give your body time to heal and regulate. Try not to TRY so hard...if you relax, it will happen.
Take a month or two to REALLY know your body. Can you identify when you are ovulating? Use an ovulation kit or track your basal body temperature. Make sure you are taking your prenatal vitamins. Get some moderate exercise. Drink plenty of water and eat a healthy, varied diet.