I tested positive for covid 19 around 20/11/2020 and i was under quarantine till 04/12/2020. on monday i was in contact with a colleague who tested positive yesterday can i be reinfected?

Reinfected : In October 2020, first case of documented reinfection with virus of COVID-19 was reported in Nevada, USA, it was fifth in World. So it is rare but possible. It is also possible that you may not get sick but transmit to others. So, wear mask, maintain social distancing, wash hands and do not meet anyone indoors for 7 days and get tested.

Antibodies: You have most likely developed protective antibodies from the first infection and the antibodies may be present for months after the initial infection. The signs are typical of a flu like illness. It is not likely that you will develop a reinfection during this time frame. If symptoms develop, please have re testing by PCR.