I have t.b. but it is inactive and i took my preventative meds already.can it ever become active even though i have taken the preventative meds?

It's Possible: If you have granulomas, then these are "walled off" nodules of the mycobacteria. This is your immune system keeping the infection in check. Your medications also assist with this, but a compromised immune system can lead to activation of the infection again. As long as you stay healthy, the risk is significantly lower. If you are concerned, discuss this with the dr that prescribed you the meds.

Preventative TB meds: If you took the treatment as prescribed and it was a long time you will probably be very safe. However if in the future your body gets compromised ie gets cancer, HIV etc there is always a chance of concern. A f/u chest xray in the setting of any prolonged cough would be recommended.

Yes: You can always become re-infected.