It might be that due to lockdown we encountered a lot fewer viruses than we normally do, so that since lockdown has eased we are all back around each other and picking up viruses and bacteria. Our system has not had a chance to build immunity in the past 3 years as it would normally. See this article: https://www.nature.com/articles/d41586-022-03666-9

Which explains that: During pandemic-related lockdowns, it wasn’t just the spread of COVID-19 being halted. Inevitably, other infections also waned, as school children stayed at home, offices closed their doors and face masks became a normal public sight. Now, with societies opened up again, infections are on the rise, have become worse or more prolific because lack of mixing in kids and adults may have caused a drop in population-wide immunity.