Your uterus is around the size of a papaya and is well out of the pelvic cavity by now, about halfway towards your navel. Yor pregnancy is definitely showing now - how exciting!
If you started your pregnancy at an ideal weight then you should gain around 10-12 kilos throughout your pregnancy. Bear in mind that this weight gain may not be proportional. You may gain just 2 kilos in the first 20 weeks of pregnancy and the rest in the short period after.
Do not start eating foods which are calorie-dense and nutritionally poor just to gain weight though! Weight gain in the mother does not necessarily mean weight gain in the baby, so just stick to eating healthy foods.