Feeling fatigue, having bruises for longer than usual (2 weeks is usual time for a bruise to heal), feeling cold, could be symptoms of decreased activity of a thyroid gland.
Since the thyroid gland plays a crucial role in maintaining the body's defenses, its low function will make one more susceptible to viral and bacterial infections (ex.having recurrent attacks of pilonidal cyst).
The cyst you have near the belly button could be a sebaceous cyst (benign cyst) or urachal cyst.
Another condition that need to be checked is diabetes.
Diabetes causes the above symptoms, too, leading to susceptibility to frequent localized infections.
Treatment of pilonidal cyst doesn't guarantee a permanent positive outcome.
Even after surgical therapy, this condition has high percent of recurrences.

Visit your physician and do blood tests for thyroid gland hormonal status and blood sugar levels!