I am 40 years with three miscarriages trying to get pregnant again very soon?

See a gynaecologist. Hi NoludweK

You should be seen by a gynaecologist in your area
Who can investigate the reason, if any, for your 3 miscarriages - and manage you accordingly.
If the 3 miscarriages happened "one-after-the-other" there's a chance subsequent pregnancies might also end in miscarriages - unless investigated.