I have dual citizenship, my U.S.?
You will face problems when trying to re-enter the US without a US passport but you wont be denied entry. So my advice is book an appointment with the passport service and get issued a US passport right after your appointment with them since you will have to explain why you need the passport sooner. Now if you cant find an appointment closer then use your foreign passport to travel. If you have your expired US passport, travel with it and when re-entering the US show CBP and explain why you are re-entering the country with an expired passport. They will let you in!