looking for a weight loss jump start..

thinking that either a "30 day challenge" workout or a short term diet would be fun to help keep some motivation. I have been trying to lose 50lbs and I got halfway there last year but lost my motivation, went through some some issues balancing my anxiety, and then I gained it all back because I reverted back to habits that I worked so hard to quit.

. I'm having a hard time getting my motivation back after failing so miserably..

does anyone have any challenges or similar things that they really enjoyed? preferably available for free because I do not have much money. but, I do have a gym membership.