Noticable signs, such as fatigue or skin pigment changes at 28 weeks?

Melasma? I assume you mean 28 weeks pregnant? This may be due to melanoma, which is sometimes known as the "mask of pregnancy". It is important to apply broad spectrum sunscreen several times daily, and follow up with a dermatologist to review your medications and other potential causes for the pigment changes. Treatment will depend upon the underlying cause.