All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no specific supplication to be said when making Ghusl from menstruation, post-partum bleeding, or Janabah (ritual state of impurity), but it is recommended to say 'Bismillah' (In the name of Allaah) at the beginning of Ghusl.
As for praying two Rak‘ahs after Ghusl, we hope that there is nothing wrong with doing this, based upon the Hadeeth narrated on the authority of Abu Hurayrah as he said:
The Prophet, sallallaahu ‘alayhi wa sallam, once said to Bilal at the time of Fajr prayer: "O Bilal, tell me about the best deed you have ever done after embracing Islam for which you hope to receive a good reward, for I heard your footsteps in front of me in the Paradise." Bilal replied: "I did not do anything for which I hope to receive good reward, except that whenever I purify myself during the day or night, I pray after that ablution as much as was written for me." [Al-Bukhari and Muslim]
Al-‘Ayni commented on this Hadeeth in ‘Umdat Al-Qari, saying: "'Purify myself' refers to ablution and it also means Ghusl."
Allaah Knows best.