please enlighten me.

Hello mommies! Galing kasi ako ng bedrest for 5 months due to low-lying placenta. Im on my 26th week na po as of today, and my OB said tumaas na po daw ung placenta ko so she told me na mag walking na as a form of my exercise 15 mins-30 mins a day. Nung nag lakad2 po kami ng hubby ko kanina, okay naman po sya until nanigas sya ng konti but di naman painful, but parang bumigat yung belly ko. Di po kasi ako sanay mag lakad ng ganun katagal, 1st ko po kanina in a long time. I would like to ask po sana if its normal? Ung feeling po is parang nag cocontract sya na hindi painful and unti-unting bumibigat. Thank you po sa mag shshare ng insights and experiences nila!!