hello.its a long time although there are chances of getting infected but i dont know after how much time post exposure you started losing weight.you are also not sure of the test.
even now you can get urself checked for HIV
test) and if the test comes negative you have nothing to get worried.
condom rupture can also lead to infection as the body fluids are exposed.
you must also get yourself examined and evaluated by a physician for other causes of weight loss
hope your query is clear.