Shouldn't really have much impact on weight, provided you are still able to go, albeit with difficulty and pain. Laxatives and laxative foods do help waste get past the obstruction.
The longer waste is in you the less well you can feel as the toxins and excess chemicals are taking sometimes longer to get out of you, this can make you feel lethargic and less inclined to be as active as you would normally be, and if you keep on taking on board more calories than you body is actually needing then yes you will put on weight, but it is an indirect cause of weight gain.
Keeping active in itself will not only burn off calories but also help food to progress through the pipe work all that quicker. So it becomes a bit of a vicious cycle if you are restricted in what you can do activity wise by being lethargic.
Have you recently had antibiotics? If yes .,,then top up your stomach's good bacteria levels again by taking probiotics for a few days. Good bacteria die with antibiotics, but are needed to digest foods properly keep hydrated - drink more than your thirst tells you to drink. Force feed yourself a tumbler full of water at each meal in addition to any other drinks you have.
Most of us tend to quench our thirst when we are thirsty, but only taking on board a few sips to wet the mouth and digestive tract a little bit. Drinking water more and more often will help you cleanse out and keep the poop on the move, and fill your tummy instead of snacking.
if there is any possibility you might be pregnant - get that checked too.
if you might have PCOs - then your body won't be processing sugar properly, weight gain can cause PCOs and PCOs then causes weight gain, unless you address the insulin problems that comes with PCOs. Again this is basically taking on too many of the foods that your body cannot process properly. This is one to be checked out with your GP.
just a few suggestions there you might want to look at.