Anyone else have this problem?

I am 18 weeks pregnant with my second child. With my first child I didn't find out I was pregnant until I was around 18 or 19 weeks. I had lost around 15 to 20 lbs before I found out with him. This pregnancy I am losing weight all over again. I think (not 100% sure because they didn't write my weight down the first visit) that I have lost around 10- 15 lbs already again. I am eating, and even when I don't feel hungry I force myself to eat anyways. The first several weeks I had bad problems with nausea that kept me from eating a lot, but that has passed. Has anyone had this problem? (I'm preparing myself for my doctor to yell at me) If you have, what did your doctor tell you to do? Noah came out fine and that was with me not taking prenatals for the first 18 weeks. I take Prenate Plus prenatal vitamins and also another prenatal that contains DHA, so I'm not hurting for a lot of the vitamins. Anyone with ideas to help me gain the weight? Thanks for your help!