There is another topic about memory problems, you might want to follow that. openHAB 3 runs out of memory / java heap space errors, CPU 100%+ after a few hours
However, if it takes 2 weeks to reach this level it will probably difficult to find the cause. You could see if you can take a memory dump of the system when it is low on memory to see what is eating up all the memory. In the topic I mentioned there are some tips on how to do that.