I am a 21-year-old female who tested positive ana but don't have an autoimmune disease; does my weight loss, bruising and night sweats mean leukemia?

Complicated: As a (+) ANA can be very nonspecific. Depending on how high your titer is, as up to 15% of the healthy population may have low positive 1:40 titers of ANA's. Also there are many other causes beyond leukemia that can cause your reported symptoms. This would require a more indepth analysis to be able to better guide you. Consider a formal HealthTap consultation otherwise follow up with your docs

Get seen: Maybe one woman in 4 has a positive ANA but seems fine. I'd stop worrying about the ANA. I doubt you have leukemia but you need a complete history and physical exam and basic labs (CBC, chem profile, urinalysis) by a competent physician. Night sweats are serious.