I Am 16 Years old, I Am Sexually Active With My Boyfriend.
I Just Found Out I Have A UTI. I Have A Big Feeling I Got It From Swimming At The Lake, I Am On Meds As of Today, but I Was Wondering If There Was Any Way I Could Help Prevent It From Spreading To My Boyfriend, But Still Be Able To Have Sex?.
Or Should I Just Wait.. . -.

Wait for it to clear.

The usual course of antibiotics is 10 days.
Surely you can abstain from sex that long.
Then you should be safe... but I would add a few days.
When you have sex, you often irritate delicate tissue enough to break the skin a tiny bit, and bacteria move in. Sure, you might have picked up bacteria in the lake with some open skin. Even a bug bite can let it in, or a scratch.
I learned this the hard way - a big bug bite left a big hole behind my knee, and infection spread a bright red rash from there to the top of my leg to my foot, and I ended up in the ER. If I had just washed it with soap and water, I could have avoided the infection most likely.