Simple Facts
If you eat more calries than you burn you gain wait. If you burn more calories than you eat you lose weight.
You are gaining weight - therefore you are eating more calories than you burn.
Two options now exist: eat less calories or burn more calories.
(P.S. Just for reference I am 16.5 stone having gained 1.5 stone since The Outlaw. I will be 15 Stone come race day next year. I can be a fat git or a thin git and I make a choice. The thin git has a food diary for motivation)
I suspect you are still eating like you are training for a marathon.
Training
Now a question - do you enjoy training across the three sports? If so great, if not consider what that will do to your motivation.
Swimming can be an issue. There was study that proved swimming made you eat more calories than you burn. Runners ate less. The only reason they could come up with was a possible lowering of core body temperature switching on a primeval hunger mode. So be extra aware of eating post swim - I am not saying don't do it but if you have only done 30-minutes then you haven't earn't much and you need to include the calories eaten in your daily allowance.
If you can only manage a 3 mile run then run three and walk another 3 (or 2 or 1) but don't go back in the house. Then at some point you will run a bit further because you may as well rather than walk it. Any mental thought that you can't go further is banished becuase you have to go further. Run 3-miles away from home if you have to. Then you will need to either sit and cry at the side of the road, or man-up and make the return journey.
Pick a 10k training plan and use that to get the running back on track.
Good Luck.
M..eface