Docz, when you lift you ate tearing your muscles up, your body is recovering and fixing those tears immediately. Your muscles are jacked full of blood pumping from your workout. of course they are gonna look and feel bigger. As soon as I leave the gym and reach behind me to fix my seatbelt I have to lift my ass out of the seat to grab onto it. It's awesome. But in two or even four days later they don't just shrink up. After your next bicep workout when you get home measure them then measure them again after a few days from working them out. Betcha they are nearly the exact same size. It's a head game you are playing with yourself. Your biceps are tiny muscles and are hard to grow, be patient. If you over train an go heavy before the muscle has a chance to recover you are wasting your work. It's like building a sand castle near the shore line and that wave keeps washing it away bro.
Also most guys over look them but for really large arms don't forget your triceps. They are a larger muscle group and they can handle large compound moves like dips, skull crushers and they will grow. Last year my arms were 17". I grew them up to just over 18" in just less than a year naturally.