Water can add as much as 10 lb. When doing a spin class you can sweat out plenty of water. Water can make up to 90% of your weight. That can change your weight by as much as 10 lb. as per Jeffrey Dolgan, a clinical exercise physiologist.
Stepping on a scale a day or two after exercise can show an increase on the scale! It doesn't mean you gained weight!
According to Dolgan "A person's scale mass is a combination of muscle, fat, bone, the brain and neural tract, connective tissue, blood, lymph, intestinal gas, urine, and the air that we carry in our lungs. Immediately after a workout routine, the percentage of mass in each of these categories can shift as much as 15 percent." Intense workouts cause variability on the scale due to factors like hydration status, inflammation from muscle damage repair (we call this delayed onset muscle soreness), even the amount of intestinal by-product or urine and blood volume.
Don't forget muscle is denser than fat( you do know a pound of fat weighs the same as a pound of muscle?) It's just that muscle is denser meaning
a volume of muscle is denser than the volume of fat, and therefore heavier. This doesn't happen over night it takes months. Your scale will show an increase but your body fat will decrease.
Ignore the scale and pay more attention to your body composition.
Ok, well body composition wise, my body fat is 4% higher and measurements are up at least an inch everywhere. I'm aware that as I build muscle the scale will be higher, the problem is I'm getting larger and my fat is increasing which is incredibly frustrating after nearly 2 years total of dedicated working out 4-6 days a week and 8 months of much more intense workouts where I've seen nothing but increasing fat and inches. With the amount of info available on excercise and health I should be seeing the opposite happening especially this far along.
Also have you had a medical check up and are you on any meds.?
if you don't have any medical conditions then try the following.
My fitness pal https://www.myfitnesspal.com/
And the following is also very good! Scooby's Work Shop. http://scoobysworkshop.com/