I'm seeing a lot of posts here and in my social media feeds along the lines of "I think I had coronavirus back in February and I just didn't realize it at the time." No you didn't. Or at least it is vanishingly unlikely that you did.
If we know anything about this virus, it is that it it causes very severe symptoms in about 20% of patients that requires hospitalization. If C-19 was widely circulating in February, our hospitals would have been overwhelmed by an illness that was causing non-flu viral pneumonia and putting a bunch of people on ventilators. Nobody would have missed this, especially since the exact same outbreak was occurring in spades in China.
In order to believe that you got covid-19 in February, you need to believe that this virus was circulating without detection despite worldwide media coverage and that you were in the extremely tiny group of folks who got this in the super-early stages before it even registered on the health care system, which we know it does very rapidly. In Bayesian terms, that is so incredibly unlikely as to be dismissed out of hand.
Sorry to be the bearer of bad news, but if you thought you had the common cold or a mild case of the flu a month ago, it was about 99% the common cold or a mild case of the flu, both of which are super-common during that time of the year. Specifically, you do not have C-19 antibodies and you should not behave as if you did.