What affects the interest rate in mortgages?

[Account Closed]

Here is the scenario. I first started out with a 680 credit score when I approached my loan officer (at Suntrust) back in March and he gave me a 3.75% interest rate, I'm still looking for a property up to now and my credit score had jumped up to 736 so I asked him if he's able to get me a lower interest rate since it's been a few months and my score had jumped up. My loan officer then tells me yes and specifically states the the rates have lowered a bit since then so he gets me a 3.25% but he gives me an origination and discount fee. If the rates have lowered, why am I getting a discount fee?

Can anybody shed a light on this, I'm an inch close to getting a different loan officer.