D.W.
Ironically, Xenical (which is the prescription version of Alli) was the first drug I sold as a pharmaceutical representative. That was several years ago, but I can share what I remember about it.
The product works by blocking 30% of your fat intake, and it has nowhere to go but out your rear end. So, almost all the side effects are GI (gastrointestinal) related.
It makes you eat a healthier diet unless you want to chance side effects. I used to hear all kinds of horror stories about people who had taken a Xenical with a fast-food meal and spent the afternoon in the bath room as the fat passed through their system.
Recently, the FDA required label updates because of concerns over some liver-related issues. I'd highly recommend speaking with a pharmacist or your doctor before using either product.
I do know that Alli has a really active online community with all kinds of personal stories. I googled using it during BF'ing, and it is not recommended according to the FDA's clinical information I could find.
There are also a lot of hormonal issues that can cause you to gain/lose weight, so don't let yourself feel like you've failed if you're doing all the right things and don't see the results you want.
I did hear a story of one lady (who did not use these products) who lost over 100 lbs and had kept if off over a year by always starting a meal with a full glass of water and really, really, really chewing each bite of food. It made her take more time (it takes the body 20 minutes to recognize when you're full) to eat.
Another really good thing you can do is to add more fiber to your diet both through high fiber foods (Fiber One has some really good products) and fiber supplements. Fiber helps you feel fuller sooner and also helps to block the absorption of carbs.
Whatever you decide, good luck! I wish you well.....I could stand to lose a good 15 lbs, and I'm having a heck of a time getting it off.