43 TTC

Hey guys. A bit about me, I'm 43 and recently engaged to a new man in my life. I have 3 gorgeous children to a previous marriage aged 25, 23 & 16. Was in a relationship for 10 years and has 7 m/c and one pregnancy terminated at 22 weeks due to complications. Am  hoping me and my fiance are more compatible at having children together. My doctor told me it could be my ex partners and my chromosomes weren't compatible. So now I am up to 4 months of trying. I have not done my body temp before so some advice would be great. Thanks in advance