It’s normal, as the others have said. I’ve had mine for years, and still sometimes i’d have it on day 1 and 2 for example, and then nothing on day 3 and then some again on day 4, and so it goes. Mine have been changing over the years in the heaviness of the flow, the number of days it lasts, the severity of the cramps, the PMS’s change, the number of days between cycles have varied anything from 28 to 60 days, so it can be normal to have all sorts of changes in any respect of your cycles over time. You can always get a doctor’s opinion if something worries you too much, but expect the unexpected. :)