Apart from the other observations in this thread I wonder if part of the issue is the work culture here. If you call in sick there is often an expectation or requirement that you will go to the GP to get a medical certificate to "prove" you're sick, and having a "cold" isn't typically an acceptable reason for not showing up for work.
I haven't had to worry about this in years but while working in retail I periodically found myself at a GP and being prescribed antibiotics when I would have otherwise stayed home to rest, if I didn't need that medical certificate.
I've recently been considering building a Shopify app(product renting) but I can't figure out if there is a demand. A similar app has <10 reviews. Do you have any advice?