Girls, I keep outgrowing my bras? Is this normal?

So I bought a 30G months ago, then I started having my boobs spill out and bounce non stop dayslater. So I bought a 30H and the same thing happened again! Now I bought a 30I weeks ago and it used to fit perfectly but it's too small now. What's happening?
Updates
+1 y
It may also be good to note that my period should be coming up soon and I feel these kinds of almost little cramps in each one.
Girls, I keep outgrowing my bras? Is this normal?
Post Opinion