running is one of the fastest ways. your body has probably gotten use to it, hit a plateau. u can try changing your routine. sprink, run, treadmill on an incline.. try kick boxing. some other forms of cardio to shake your body out of its comfort zone. the wt gain u mentioned can be water. if u have been eating carbs or salt they can both add water wt.

there isnt a safe way to lose wt fast. itll be mostly water and u will gain it back. just up the cardio, different forms. really push the major muscles. legs back abs that burn fat. its ok to take breaks from exercising too. your body will stop losing wt if you are doing too much.