Which model and carrier do you have? The April security patch fixes some nasty (full phone takeover) vulnerabilities, so Samsung and most carriers seemed to be in a hurry to get that one out with little delay. Last week, the unlocked US model (SM-N960U1) even got the CSD1 firmware update (with the April 1 security patch) just 10 days after it got the CSC2 update (March 1 security patch)--two updates in one month, less than two weeks apart.
So the first thing you should do is figure out whether it's your entire model/carrier that's out of date, or whether it's just your own phone that hasn't been seeing the updates. Try to find the online firmware release notes for your phone.