Got a positive ovulation test on 26th feb. then after 16dpo, pregnant test negative, and again a positive ovulation test . ?

Normal?: It is more important that you had a positive surge of lh (the hormone detected by the kit) at mid-cycle. I would suggest that you also take note of any other symptoms (cramping / cervical discharge) that you might notice. Yes there is a surge of lh around ovulation, but there is also a slight rise back to baseline at about day 26-28 that the test might be detecting.