I recently lost a lot of muscle due to not eating properly for about a week. now i feel soreness and quite weak. is this normal ?

Yes this is normal: More likely you were not consuming enough calories. Simply eating the wrong foods for as short a time as one week will not cause muscle loss. However if the body is not fueled properly weakness is a natural result.

Muscle Fatigue: Generally, one should not lose a lot of muscle mass in a week of under eating, unless you really starved yourself. If you did, it is typical to experience soreness and fatigue, but, more cogently, it is important that semi-starvation for a week at a time is not a pattern that you plan to repeat. Once you resume a normal, healthy diet, your strength should return. If not, consult your doctor.