Exercise

I need to do strength exercises frequently for my physical therapy (my shoulder) but lately, my arms are too tired to do them because of all the work on the house. I got more plastering done today since my husband was home for President's Day. I was supposed to do my weights and now I shouldn't push it too hard or I'll aggravate my shoulder again. I do feel a little guilty for not getting the workout in but I obviously worked hard today plastering, just in a different way. What makes you guys skip your workout? Just rest days? Hectic lives? I feel like once I have kids, I'll never get a workout in so I might as well cram them all in now (I'm not pregnant nor planning on it for a couple years but still).