The weight gain is mostly important in the second and the third trimester of pregnancy so I guess you can still wait a couple of weeks and watch your weight gain along with having a regular balanced diet recommended for pregnant women.

anaher,
Weight gain is slow in the first trimester and the weight gain increases during second and third trimester. I also had a similar concern during my pregnancy and my doctor told me so. Later in 2nd and 3rd trimesters my weight gain was ok. SO, you can wait but do talk to your doctor about this.

During first trimester many women are not able to gain much due to morning sickness. Its lucky that the foetus does not need much calories at this time. But from the beginning of 2nd trimester its very important to have a proper diet so as to gain approx. 1/2 kg per week.

Some of the ways you can gain weight are
- Eat smaller and more frequent meals
- If you find it easy you can add calories by drinking some healthy drinks like smoothies

In addition what has been mentioned by dikoy I would suggest additing some supplements to your food. Like if you are having some milkshake/smoothies etc. mix some protein powder in it. Take some multivitamin supplements.

Add some cheese and nuts to your meals for extra protein. This has been helpful for me. Give it a try.

For me eating small amount but frequently has helped. And also add a lot of protein rich food in your diet. Cheese can be good to add to your diet.

Thanks for all the feebacks. Is it advisable to have nuts during pregnancy. Someone was suggesting me not to have lots of nuts.

Just eating is not enough. Along with eating proper exercise and rest is needed.
Try to get do some yoga it has helped me a lot during the whole of pregnancy.

Anything in excess will not be good. But moderate amount of nuts will be very nutritious as long as you are not allergic to nuts.