Why does weight loss come in cycles?

I have been losing weight since November 2013 and have lost 34lbs during this period. My question goes to the odd drops in weight that occur over this period. First, I have been consistent with the diet with very few exceptions. I was 274lbs and 6'1" so my "normal" weight is to be under 190lbs. My goal was to first achieve 239lbs which is the threshold from obese to over-weight.

On three occasions during the last 5 months I have had the short cycles of significant weight loss (e.g. about 6lbs in less than 2 weeks) followed by prolonged weight stabilization (less than 1lbs in 2 weeks). I feel great and have no other symptoms except this last cycle my bowel movements have reduced to once every other day. I am also checking my sugar levels which range from 94 to 110 which seems good.

Is the significant drop experience normal or a symptom of bad dieting or something else. I do plan on talking to my doctor next Monday and having blood work done to make sure there is nothing medically wrong, and I don't believe there is a medical related issue given I just had a full body scan and blood work done 4 months ago when I started the diet.

Your thoughts and comments would be appreciated.