Thank you for consulting with Doctorspring. I understand that you have bought a Sphygmomanometer for home use and that the readings over a week have been high. The normal blood pressure is taken to be 120/80 (Systolic BP: 120 mm Hg and Diastolic BP: 80 mm Hg), so, even if your machine is showing a very high level, I think you should first get your BP tested by a Doctor. This is because the machine you purchased may not be calibrated perfectly unlike the ones available with the Doctor.
A few things to be followed while measuring your BP is that ensure that you are sitting comfortably on a chair with the apparatus at a table nearby, ensure that you have a cuff of the adult size and that the cuff is fixed firmly so that it doesn't allow more than one finger between the cuff and your arm. Usually high blood pressure doesn't present with any symptoms but your headache may be due to the high BP if it is indeed high.
Yes, you should see your GP to have you blood pressure checked because the values you are getting on your apparatus may be right. Also talk to him about your headache. You're overweight for your height and you should be doing something about that too. So, talk to your Doctor about some lifestyle changes you may need. Hope this information was of use to you.