Resistance training does not make you bigger! Creating a calorie-surplus where inputs exceed outputs makes you bigger. Regular (and progressive) resistance exercise merely provides a signal to divert some of this calorie-surplus to muscle growth.
Depending on your body-type creating a calorie-surplus is easier said than done. For ectomorphs like me it can be a real struggle. Bottom-line though, if the scale weight isn't shifting upwards you probably aren't eating enough food.
Here are some ideas to change that:
Eat Bigger Meals - Larger portions served onto larger plates. Simple in theory but uncomfortable in practice if you are unused to eating substantial quantities of food. One solution is to slowly ramp up the size of meals. This allows your digestive system to adjust and adapt at a more reasonable rate.
Eat More Frequent Meals - Can’t stomach bigger meals? Try eating more frequent meals. Or for maximum energy intake do both! Like before this can take some getting used to.
Increase The Energy Density Of Meals - Eating bigger salads won’t cut it. You need to start ramping up the energy density of each meal. Allocating more of your plate to energy dense foods like starches and fats is a good place to start. Or find ways to add calories to existing favorites. For example using a food blender to turn nuts into powder which can be mixed into a bowl of porridge. This takes no extra effort to eat but significantly ramps up the energy-density of the meal.
Liquid Meals - Homemade super-smoothies offer an effective way to pack a lot of extra nutrition and calories into your day. It's much easier to drink calories than eat calories. Smoothies can be consumed alongside existing meals (more calories per meal) or consumed between meals (increased meal frequency.)
Of course not everyone needs to do all of the above. For some just adding an extra meal to their day might be enough to tip the scale towards weight gain. See what works for you!
Last but not least... trying to sustain an unnaturally high bodyweight by feeding your body more calories than it wants or needs is not without its drawbacks. Like anything taken to the extreme, the negatives can start to outweigh the positives.