I had the iud for 5 yrs. removed this past december. then on birth control until the end of april. my heavy period only lasted 2 days july/aug. why?

Menses: It is not unusual after using an IUD, especially Mirena(which I am assuming because it was in 5 years) and the OCP to have periods different than you are used to in the past. They may return to normal for you or they may continue to be what sounds like shorter.

Periods vary: but 2 days of heavy, with 2-3 more days of light is exactly average. Hormonal birth control pills work because they have low doses of the hormones that regulate the cycle, but too low a level for it to work correctly with ovulation, etc. The cycle runs at normal time, but is generally less heavy. Can take a couple months for regular cycles to start up in some aftr stopping OCP's