I don’t believe that it’s possible to diagnose MS from DNA.
Having had a brief look, it seems that the HLA-DRB1 gene does mean that you might be marginally more likely to develop MS. But genetics plays only a small part of the development of MS.
There are, as Plushpear said, identical twin studies that show definitively that genetics are not the whole story. In fact, as https://mstrust.org.uk/a-z/risk-developing-ms shows, the lifetime risk of getting MS as the identical twin of someone diagnosed is only 1 in 5.
Other factors contributing to the development of MS are environment, exposure to viruses, geographic location, gender, and many others. In fact, growing up in Africa makes it less likely that you have MS. That would probably explain why you’ve not found anyone else in Malawi with MS.
Have a look at https://mstrust.org.uk/news/views-and-comments/ms-hereditary-or-not-0 This will give you a better idea.
Considering you’ve had a negative MRI, the presence of a specific gene is irrelevant.
To me (albeit not a doctor, just a generally well informed person with MS), you have not been diagnosed. That’s not to say that you definitely don’t have MS, but that it’s certainly not proven that you do. The diagnosis of MS is usually based on the McDonald Criteria (McDonald criteria | MS Trust)
I suggest that you see a neurologist. Don’t base your health problems (about which you’ve said nothing) on MS until and unless a neurologist formally diagnoses it.