Hi I I did understand your concern sir. From your problem it seems that you have a condition known as acanthosis nigricans. This is manifested by skin darkening around armpits and skin tags and it is associated with hormonal issues like diabetes mellitus. Atleast a basic test like fasting blood glucose that can be done very cheaply is what i would advice to rule out diabetes. You can maintain your blood glucose by a healthy diet and aerobic exercise. If diabetes is ruled out there are other things that can cause acanthosis nigricans it could be due to underlying malignancy, but it is infrequent. Also heart palpitations can be due to excess coffee, anxiety, hyperthyroidism or internal heart problem and it needs to be assessed separately in your case. I hope this helps. wish you all the best. thank you for choosing healthcaremagic.