I lost interest in having sex with others... but that's because my attention is on my 'significant other to be'.
Still, in your case, it's possible it's a combination of factors.
Being overweight can cause depression which in turn could translate into a lack of interest when it comes to multiple aspects... sex included.
Though it may also not be the case.
If you have masturbated on a frequent basis for example, you could have reached a point of 'saturation' (porn can do this as well).
Perhaps you could try shifting your attention to something else.
Maybe you could try losing some of that weight, exercise, etc... it might help restore your sex drive (a lot of individuals who don't exercise on a frequent basis suffer from lack of sexual drive - then again, it can also be a pure mental thing - psychosomatic response).