hi, there are veaous things you can do.
for a start leafy grans are a grate source of iron, along with vitc and folic assid which help the uptake. it is currently watercress season which is a good source esspecly if it is proper hampshire watercress (grown in the troditonal way) other greens which are good is anything in the cabage family, but don't over cook them. if this is a bit dounting the herb time is a good place to start, add leves fresh or dryed to your normal cooked food or salads and the high iron dencity of time will show in your heath.
also as to gaining waight i would sugess try increasing your calery intake. try useing butter insted of spreads and increasing your partions slightly. having two or three snacks a day, nothing big just a cearl bar or a peace of frut, or teat yourslf to the stiky you like at least once a week. but do this conbined with proprtante exersice which will help you put the waight on a mussle and lean fat which is heathy rather than not.
feel free to pm me for more about heaty veggy eating