I'm going to go with growth spurt and coincidence. LOL You won't have been taking Noriday for long enough for it to build up in your system AND milk doesn't just disappear overnight, contrary to what some people will tell you. Noriday has had some reports of interfering with milk supply if started before 8-12 weeks but not anything if started later as far as I know.
Just FYI....with DS2 his 12 week one merged with his 16 week one so this one could go on slightly longer than a previous growth spurts.
Just go with it and things should be fine because this is a 'biggish' spurt and it will mean that you start to produce enough milk to respond to his emerging needs.