Problem concentrating during Vipassana meditation

I am having trouble maintaining concentration for long periods of time. I make my breath slightly hard and then pull my mind back to it and then carry on as normal. But it's quite hard to have a long sustained period of breath observation. Once maintained I try to move from head to feet taking large body parts such as head, abdomen, arms and legs. Do this for a while and then the mind wanders away again and come back to breath. At times the mind wanders for long periods of time until I realise it's wandered away. I haven't been able to penetrate and observe smaller, subtler sensations since a year now. I know it's harder to do this at home than at a retreat but I am wondering if this has something to do with my Silas. Although they are not the most perfect I do try my best to maintain them. Anyone stuck in similar phases and overcame it? Suggestions are welcome. Ps. I am a Goenka student and very faithful towards it and have never tried anything else and don't intend to as I am very happy with the results this technique has brought me.