Reported cases is not a really useful statistics if every suspected case isn't tested and the number of tests per day are increasing, both of which are true for most countries - Sweden included.
The more relevant concrete statistics is number of patients in ICU and number of deaths, both of which are slowly decreasing in Sweden.
As for the strange 7-9 cycles there is a simple explanation for the 7-day cycle seen in most countries (Sweden is just a bit more extreme). It may be deep kept secret, but I will reveal it anyway:
Seven days is the work-week with less work during the weekend. Additionally during the spring there are a large number of extra holidays in most countries (Easter etc, first of May, VE and related national holidays).