Definitely change your focus and take a break from working out.

Instead of focusing on your scale weight, why not focus on your BF% and let that determin your scale weight? 20% BF is healthy, attractive and attainable. If that puts you at 118 lbs if you do not gain any more lean mass then so be it. If you weigh 118 lbs with 20% BF and if you weigh 118 lbs with 26% BF you're not going to be the same size - fat takes up more volume / space than muscle does.

If you only seem to lose weight when you stop workingout it could be a sign you're working out too much and/or not eating enough. Workouts create a calorie deficit, if that deficit is too large your body becomes stressed and holds onto fat and water. Also, if you've been consistently workingout w/o a break for over 4 months it's time for a week off - the stress and lack of recovery can lead to overtraining and hinder progress (it can also make you sick)

I'd strongly suggest you hold onto all the lean mass you can - and get more if possible. It's the lean tissue that raises your metabolism and makes you leaner in the end. Muscle eats fat, the more you have the more fat gets eaten and the more calories you can eat to maintain your current weight. If you're building lean mass it's because your body needs / want's it. Some of us are predisposed to build it easier than others, some have to fight tooth and nail. Eating adequate calories and protein is how you maintain mass - throw in some resistance work and keep cardio from becoming excessive and you've got the mix that works for most of us.

Also, take all those online calculators with a grain of salt - they're OK for measuring progress though.

Cheers,
Nat