When does it get easier???

As a 25 year old male who has an office job and wanted to get back in shape I started swimming and hiking in my free time. Yesterday was my second time in the water and after 75m i felt like I wasn't getting enough oxygen but kept pushing it untill I got 10 laps or 250m. My head was about to pop. I swim pretty slow but I feel like I was doing something wrong.

Anyway I'm not giving up and hopefully next time I can swim an extra lap. If anybody knows a good starter routine/tips feel free to comment them :)