Please help me starting to get a lil worried?

i was just wondering im coming up to 2month not having my monthly and getting a bit worried ive done loadsa pregnancy test but theyve come back im not pregnant. i have put a bit of weight on and some days feel quite nausea tired dizzy. i did use to be on the depro jab but when i went to see my nurse about this as i stopped using the jab last year and had my first period feb was on for a week and about a month later was on again so was regualr but since then i havent had one i asked her is this why iv not come cause of that jab but she said would not affect me as im sorta in a routine again if you get me so ive left it a few weeks and still not come on im justt starting to get a bit worried thats all hope some one can help me cheers