Confussed?

Can any1 help me? I have type1 diabetes and I have had it for 16years! I have been 100% fine with it and hbac1 has been good too! But just recently my levels have been really weird! For example last night before tea my sugar level was 10.8 so I had 5.5 units of insulin, for tea I had a Sunday roast which was 2 Yorkshire puds, 2 roast potatoes,2 slices of pork, veggies, 2 battered parsnips, mash potato and sweede mashed. Then a glass of rose wine and dessert was meringue nest with cream, ice cream and fruit! Very filling!! Then about half an hour later my sugar level was 5.5 so I had the small bottle of Lucozade and half an hour it said 5.8 so then I went to walk the dog came back and it was 3.4? How can this be?? This never used to happen? But happens alot recently? And recently I have lost a bit of weight so no idea if this has anything to do with it?

Thank you! Yes I have a 24 hour long acting injection of lantus then novarapid before each meals! I did down my long acting down by 1 unit but then started having highs! I now have a new pen which does half's so could give that a go! Thank you! Its just so annoying! I used to be fine no problems at all but just recently is been horrible!