Through lockdowns and other severe changes to daily life, almost everyone is affected by the COVID-19 pandemic . Scientists and medical doctors are - among others - mainly interested in researching, monitoring, and improving physical and mental health of the general population . Mobile health apps (mHealth), and apps conducting ecological momentary assessments (EMA) respectively, can help in this context . However, developing such mobile applications poses many challenges like costly software development efforts, strict privacy rules, compliance with ethical guidelines, local laws, and regulations . In this paper, we present TrackYourHealth (TYH), a highly configurable, generic, and modular mobile data collection and EMA platform, which enabled us to develop and release two mobile multi-platform applications related to COVID-19 in just a few weeks . We present TYH and highlight specific challenges researchers and developers of similar apps may also face, especially when developing apps related to the medical field.