Is it possible i could still have malaria even after tests have come back negative?

Yes: Parasites detection may lag behind symptoms of malaria sometimes for many days, if initial test is negative, it should be repeated every 12 hours until malaria is detected or ruled out.

Yes: certain types of malaria do not have enough parasitemia (parasites in blood) to be seen, so the test may be interpreted as negative. further tests or repeated with special timing may be necessary to see the parasites.