This is the most common problem with new and novice swimmers, and often swimmers that have been struggling for years. Time to turn off the busy kick. Lot's of kick is the most common culprit and where the o2 demand is greatest (the legs). Quiet the kick. If your hips are low increasing drag profile, effort goes up crawling your way across the length. You will need to learn the skill of balance in both drill and freestyle to build a solid foundation that doesn't trigger fast arms and busy legs to remain stable.
The Ulta Efficient Freestyle Tookit
(eBook and videos) is the best place to start with the progression building a solid platform, *Balance* that will allow you to be streamline and slip through the water with far less effort than you are currently experiencing.
Enjoy the journey!