If You Are Slowly Loosing Blood And No Internal Bleeding

If you are slowly loosing blood and no internal bleeding is found, where would you look next to find the cause? This is in an 81 year old lady with A FIB, high BP, high cholesterol, dizzy spells that almost make her pass out. She has been taken off Eliquis blood thinner, while on the thinner she lost 2 units of blood in 1 month. After coming off blood thinner and receiving 2 units of blood, within 1 1/2 weeks her blood is down again, but not enough for another transfusion. She has had an upper and lower scope. There was no loss of blood found.