Rapid Weight Fluctuation

New poster here.  I've been having issues with my listed weight over the last week and could really use some advice and feedback.

I started exercising at the end of April regularly for the first time in years, and had lost a considerable amount of weight.  Or so I thought.  Last Tuesday I was down to 319.  I decided to weight myself again on Wednesday just because I wasn't going to be there Thursday (I usually weigh myself Monday and Thursday).  To my surprise, I was up to 330!  I weighed myself again today and was up to 334.  Now granted Thursday-Sunday my calorie intake wasn't as great as it had been, but it also wasn't awful either.  My daily high during that period was a little over 3000 calories.  

Thinking that maybe the scale at the gym is just not working right, I bought a new scale for home today.  This scale has me at 343, only 2 hours after I weighed in at the gym at 334.

I'm really at a loss for what's going on and what is actually accurate and whether all the weight I thought I had lost, I actually lost.

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