First of all, I hope you are well soon.
Secondly, you do not have to test negative to get home. You either need to test negative or have a certificate of recovery. You may receive a certificate of recovery 5 days after your official positive test if you are symptom free or your symptoms are decreasing.
First step: Make sure your covid test is a documented test vs. a home test you did on your own. You need a documented test (it can be a proctored home test) to start the clock ticking.
Second step: Understand the requirements of the country you are visiting. Here is the website for the UK
https://www.nhs.uk/conditions/coronavirus-covid-19/self-isolation-and-treatment/when-to-self-isolate-and-what-to-do/
Third step: Decide how you will get a certificate of recovery. Three main ways. 1. Contact a doctor in the host country 2. Contact your doctor in the US to see if he/she will provide one. 3. Use a telemedicine service.
Here is a link to one and the directions for using it are pasted below
https://quick.md/documentation-of-recovery/
These were the directions I received from quick.md when I wrote them to confirm an individual who was overseas could receive the documentation of recovery from them. The bold print is to highlight some key ideas. The words are a direct quote.
"Thank you for reaching out.
We can provide you with documentation of recovery. You need to present your official written positive result during your appointment. We are currently ONLY accepting COVID results via PCR, Antigen, or Rapid. PROCTORED at-home test results may be accepted if you are able to provide printed results or a soft-copy. Test must be taken within 90 days from your appointment date. Home test kits and antibody tests will not be honored.
Please check with your airline of choice and destination if this would be accepted and if there is any more information they wish to be included in the certificate to avoid any issues. As per the CDC's new guidelines, you can be seen on the 5th day after you were tested positive of the virus provided you are asymptomatic or with improving symptoms.
You can book a video appointment by creating an account here or you can log in to your QuickMD account if you have already created one, schedule an appointment by finding a time that best works for you. Choose Urgent Care as the Appointment Type, Doctor's Note as the reason. You need to use your US home address and US contact number in your account to be able to see a provider. Each person requiring the note is to create an account with QuickMD and book an appointment under their respective accounts.
Within a few hours after the consultation, the doctor will email you the document to your email address as a PDF."
Fourth Step: Continue to test every day with a home test to see if you turn negative prior to needing a certificate of recovery. If you do, then get an official test and you are good to go.