I usually reserve the term feedback loops for physiological processes, like control of temperature, which you’ve mentioned. The best example of a positive feedback loop is during labour. As the baby’s head pushes on the cervix, this signals to the posterior pituitary to release more oxytocin, which increases uterine contractions, and so the cycle repeats.
I wouldn’t have called atherosclerosis a positive feedback loop, although it’s certainly a vicious cycle.
In atherosclerosis, there is some insult or trauma to the endothelium (lining of blood vessels) which allows LDL to enter the inner lining of the arterial wall. This LDL is oxidised, which is pro-inflammatory, which recruits inflammatory cells. These inflammatory cells release reactive oxygen species and pro-inflammatory mediators which recruits more inflammatory cells, and so the cycle continues.