I got a doubt during Sajdah, while praying my Asr prayers, about whether I was in my third or fourth Rakat. What should I have done in that situation?
You should take it as forth Rak'at and complete the Salaah accordingly but you must pray immediately after Salaam, one Rak'at of Salatul Ehtiyat in which you recite Sura Al-Hamd only then do Rokoo' and Two Sajda then Tashahhud and Salaam.
Wassalam.