Haemorrhoids are always in your arse, and then straining can make them come out and thats what people call the 'bunch of grapes'. But really, they are nothing more than enlarged blood vessels. You can get rid of haemorrhoids by squating when you 'pass a stool (so like a french toilet stance). This reduces the stress and you need to push less, and thus less strain, and symptoms improve.
It's definitely the lifting causing this, and i would say no cause for concern. Just take it easy, as to physically burst blood vessels needs quite a lot of strain, thus, you may be slightly overdoing it.