Back ache or cramps🧐🧐?😪

My friend and I went for a walk today and was fast paced! 30 mins but fast. Am now in pain and so confused as I don’t know if it’s my back/waist or am cramping! Been in bed the last 4 hours and so scared I hurt myself. Am 28 weeks today and praying that what I am feeling is just the aches after a walk. Anyone feel such pains after a walk??