helpful tips needed!

It's hard to answer this question without more details.

Three weeks isn't a lot of time and you're still within the margin to be seeing some water weight retention if the exercise is new or you're at that TOM in your menstrual cycle.

Other than that, the most common problems we see come from underestimating calories eaten and overestimating calories burned.

Opening your diary might help to get you more specific advice if you're comfortable doing so.

You're logging everything you eat? Including condiments, cooking oils, veggies, cheat days, etc? Are you using a food scale, measuring cups, or eyeballing your portion sizes? Most people can be off in their estimates by several hundred calories when they eyeball portions. Measuring cups are better, but a food scale is going to be the most accurate.

http://www.myfitnesspal.com/topics/show/1234699-logging-accurately-step-by-step-guide
http://www.myfitnesspal.com/topics/show/1290491-how-and-why-to-use-a-digital-food-scale

And make sure that you've calculated your calorie goals appropriately. Remember that these are just estimates. You may need to play around a little to find what works best for you.

http://www.myfitnesspal.com/topics/show/1080242-a-guide-to-get-you-started-on-your-path-to-sexypants
http://www.myfitnesspal.com/topics/show/819055-setting-your-calorie-and-macro-targets

If you're exercising and eating back your earned exercise calories, be sure that you're using accurate estimates of your burn. MFP and gym machines have a tendency to overestimate certain activities, which can cause you to eat back more calories than you need to. Even a heart rate monitor isn't 100% accurate. If you're eating those extra earned calories it might be a good idea to eat only 50-75% of those.

And there's something to be said for the fact that some people just burn fewer calories than the generic equations predict. If that's the case for you, you may need to adjust your calories a little lower until you start losing again.

I would suggest to first Look at how much fresh fruit and veggies you are eating. For myself I love to eat volume so I aim to eat 65-70% of each meal as vegetables and fruit. I try to only use no fat or low fat dressing on salads. We should visually see lots of veggies. I try only eat 2 servings of grain per day. like 1 toast in the morning, and 1/2 baked potato at night. Try eating fruit for your dessert.
(I like a paper thin spread of low fat peanut butter or PB2 on a banana with 45 calorie almond or coconut milk.

Also, try eating some meals just a giant salad with a protein shake.
The fluid will fill you up!
If you love spice like Mexican salads here is one of my own dressing recipes:

Mexican Salad Dressing

(You can make this thick for a dip or thin for salad dressing)

In a Blender:
½ can Chick pea – rinsed
3-4 tbsp water
1 clove fresh garlic
A squirt of fresh lemon
1/8 c vinegar of banana peppers rings
1 or 2 Tbsp Taco Seasoning Spice
2 Tbsp Sesame Tahini OR 4 Tbsp raw sunflower seeds
2 Tbsp Olive Oil

Blend till creamy. You may want to add water one Tablespoon at a time for desired consistency. I love Mexican food, and I love the dressing because it is high in fiber, protein, and creamy. I make this at least once per week.

Let me know if you like it.

TO YOUR SUCCESS!