Having been there many times myself, I think I'd look to rule out a medical cause. An underactve thyroid or insulin resistance can make it extremely difficult to lose weight. Testing just involves blood work in the morning of TSH, Free T4, Free T3, thyroid antibody test, insulin, glucose, and an A1C.
Be very contiou of your sodium and potassium intake. Sodium causes us to retain water and potassium is wha balances it. Sodium/Potassium should be 1:6 ration but as you can look into is sodium is in everything and potasium gets very easily depleted from the body especially from medications.
Make sure you are eating 5-6 times a day. Make a fist with both hands and put them together and that is the siz of your stomach, approx, so be careful of portion control.
How long are the cardio sessions you are doing? What type of cardio? What are you keeping your Hear Rate at?