Why is it that some days are hotter than others, even though there are no clouds in the sky .?

Question

Does it have something to do with the angle of the sun's rays.

Answer 1

For a given latitude the angle of the sun will be the same everywhere on a given day, and the change from day to day is pretty gradual. It will not account for the variations that you describe.
Instead, look at the air mass that is covering your spot at the moment. Where did the recent weather patterns bring it in from. Does it have a high moisture content, (your perspiration will not evaporate as well and you will feel hotter if it is high)?
Did it form over a warm region or a cool region?
Do you have a local condition such as a mountain breeze or a sea breeze?
These factors can all cause variations on a day to day basis.

Answer 2

Yes;with respect to your place, the sun's position(latitude wise) is changing everyday.If it is approaching you,days will be getting hotter and if it is moving away,days will be getting colder.
Somtimes prevailing winds also play a role in changing the temperature.Winds from a particular direction may bring dry air and thereby increase the temperature.Sometimes they may bring cool air(example: sea-breeze) reducing the temperature.Even sea-breeze starts at different timings over a particular coastal station with the result,maximum temperature recorded varies every day.