Tips for weight gain..

I am 17f recently lost around 10kg due to some diet I m following it because of some diseases. I cannot eat non veg , bananas, oil , chickpeas, brinjal, potato....Is there any way I can gain weight while still being on my diet...with weight I have also became very weak.....I want to gain both strength and weight

My current weight is 42.5 and my height is 5'1