I'd say that having the in-laws staying is a great reason to get out running: 1) there's someone in the house to look after the mini Dippys and 2) you'll probably be desperate for some personal space!
I've been running for just over a year now and trust me, even more experienced runners have off days. Last night I really struggled with a route I can normally run easily. All sorts of factors affect whether you have a good run or not: the weather, your mood, how tired you are, hormones, how hard your last run was ...
Don't give up: once you become hooked you wonder how you lived without running. Seriously, since I became a runner I've noticed an increase in my self-confidence, I generally have more energy, I have a fit, toned body which I'm happy with, I feel more positive about any problems I have to deal with and I can eat whatever I like without putting on an ounce!