Cycle changes?

Melissa • 25 and pregnant with our first little Peanut!
So I'm 24 and in the past few months my period went from extremely heavy to barely there. 
​I've taken probably 20 preg tests and all came back negative. 
​Think this is normal? My doctor doesn't seem fazed by it. 
​I'm concerned though, if my cycle is irregular then it's going to be difficult to tract ovulation.