Your LMP STARTED on 28 November?
You can not get pregnant from anal sex. Sperm would need to get INTO, not just near, but INTO your vagina.
If so you had anal sex on day 4 of your cycle. You'd be extremely unlikely to get pregnant even having vaginal sex then. Sperm can survive UP TO about 5 days. Most women ovulate sometime between days 11 and 16 of their cycle.
You had sex with your best friend on day 7 and later. He is the likely father. If you ever had sex "twice in a row" and he didn't use protection when entering then any semen, not precum but semen, in his penis would be squeezed into your vagina.
You should have had a period sometime around the 26 of December but did not. You were likely pregnant then.
Also, it takes about two weeks for a pregnancy test to be able to determine if you are pregnant - sometimes it takes longer. It's only been 12 days (today).
Again, you had anal sex with your fiance.
Your best friend, not your fiance, is the likely father. A DNA test can confirm. You can get test, non-invasively, as early as 9 weeks. They can extract the babies DNA from your blood. Both partners would need to provide a sample as well. Google "non-invasive DNA test."