Beer has strange mineral watery flavor to it

I brewed an American what a month ago, bottled it 2 weeks ago. It has an unpleasant mineral water flavor to it. My dad also tossed in some gypsum when I wasn't looking and was wondering if that could be the culprit. I have tasted this same flavor in some of his other beers and never in mine without the gypsum however, my other beers always have some steeping grains or partial mash component. Otherwise the recipe is as follows:

The recipe is as follows
3lb extra light DME
3lb wheat DME

1oz Cascade 5.5%AA 60min
.75oz Liberty 4.0%AA 15 Min
.25oz Liberty 4.0%AA 5 Min

SG: 1.048
FG: 1.016

Does it seem like the gypsum could be at fault or is my recipe a bit off?

Well, it's either your brewing water, the gypsum, or the hops. I'm not familiar enough with Liberty hops to say. If you've brewed with the same water with different (and more pleasant) results, I would say the culprit is the gypsum

Your water source COULD be the culprit. Some water sources change chemical composition seasonally, while some municipalities change the source of their water for various reasons. This could possibly be a culprit.

BUT, I lean towards the gypsum addition your father made. What is "some"? If he threw in too much, you could be tasting gypsum itself, or it could have changed the profile of the hops. Gypsum accentuates hops in beers.