Hey alvena, im totally in the same boat as you! Im also a medical student, age 20, 5'6'' and a uk size 12 (used to be a 16/18 2 years ago!).
my mum is always at me about my weight and is constantly telling me that no slim handsome doc will want to marry me if im this big. she also keeps reminding me how 'smart' she was at my age. its not only her though, all my friends are slim and very petite, they call me the guy in the group. they dont mean it in a nasty way but it still hurts.
but they are always surprised at how much attention i get from guys and aunties-with-sons alike, especially because im a hijabi and dress pretty plainly. its all about how confident you are about yourself and how you carry yourself.
if you are going to lose weight do it for yourself not for your mum, a guy or anyone else! you said you are trying to lose weight, i would advise that you do it slowly because that way you wont put it back on again and do plenty of exercise. in the meantime wear heels and dress smartly...always helps the figure.
also you need to talk to your mum and family about it and that they shouldnt put off rishtas because THEY think your 'moti'. the 'right' guy will like you for who you are and not what you look like! your only 22, you need to concentrate on graduating and kickstarting your career first.
i dont blame your mum either, after all mothers worry about their daughters future and dream of their wedding day from the day they are born. so try not to worry because that will only make things worse, channel your stress positively to motivate you! if your anything like me worrying leads to binge eating.
remember 'beauty is in the eye of the beholder'
BTW which uni are you at?